James N. Bull

• BSc (Hons), PhD
• Associate Professor at University of East Anglia

Betaine-30 is well-established as a standard dye for solvatochromism and has long been studied by ultrafast spectroscopy. Electronic excitation leads to rapid intramolecular electron transfer, while the decay of the resulting state corresponds to back electron transfer to the electronic ground state. Thus, Betaine-30’s photophysics offers a route t...

Indene (C9H8) is the only polycyclic pure hydrocarbon identified in the interstellar medium to date, with an observed abundance orders of magnitude higher than predicted by astrochemical models. The dissociation and radiative stabilization of vibrationally hot indene cations are investigated by measuring the time-dependent neutral particle emission...

Incorporation of fluorescent proteins (FPs) into biological systems has revolutionised bioimaging and the understanding of cellular processes. Ongoing developments of FPs are driving efforts to characterise the fundamental photoactive unit...

Betaine-30, is well established as a standard dye for solvatochromism, and has long been studied by ultrafast spectroscopy. Electronic excitation leads to rapid intramolecular electron transfer, while the decay of the resulting state corresponds to back electron transfer to the electronic ground state. Thus, Betaine-30’s photophysics offer a route...

An electrospray ion source has been coupled to a cryogenic electrostatic ion-beam storage ring to enable experimental studies of the fundamental properties of biomolecular ions and their reactions in the gas phase on longer timescales than with previous instruments. Using this equipment, we have measured the vibrational radiative cooling rate of th...

Several small polycyclic aromatic hydrocarbons (PAHs) with closed-shell electronic structure have been identified in the cold, dark environment Taurus Molecular Cloud-1. We measure efficient radiative cooling through the combination of recurrent fluorescence (RF) and IR emission in the closed-shell indenyl cation (C$_{9}$H$_{7}^{+}$), finding good...

Indene (C$_9$H$_8$) is the only polycyclic pure hydrocarbon identified in the interstellar medium to date, with an observed abundance orders of magnitude higher than predicted by astrochemical models. The dissociation and radiative stabilization of vibrationally-hot indene cations is investigated by measuring the time-dependent neutral particle emi...

Infrared (IR) cooling of polycyclic aromatic hydrocarbon (PAH) molecules is a major radiative stabilization mechanism of PAHs present in space and is the origin of the aromatic infrared bands (AIBs). Here, we report an anharmonic cascade model in a master equation framework to model IR emission rates and emission spectra of energized PAHs as a func...

2-Cyanoindene is one of the few specific aromatic or polycyclic aromatic hydrocarbon (PAH) molecules positively identified in Taurus molecular cloud-1 (TMC-1), a cold, dense molecular cloud that is considered the nearest star-forming region to Earth. We report cryogenic mid-infrared (550–3200 cm–1) and visible (16,500–20,000 cm–1, over the D2 ← D0...

Kaede is the prototype of the optical highlighter proteins, which are an important subclass of the fluorescent proteins that can be permanently switched from green to red emitting forms by...

The recent discovery of cyano-substituted aromatic and two-ring polycyclic aromatic hydrocarbon molecules in Taurus Molecular Cloud-1 has prompted questions on how the electronic structure and excited-state dynamics of these molecules are linked with their existence and abundance. Here, we report a photodetachment and frequency- and angle-resolved...

Molecular anions are appealing targets for study because, compared with their neutral and cationic counterparts, they can be probed with conventional laboratory lasers without the need for multiphoton ionization schemes, and they provide spectroscopic details on the corresponding neutral molecules. Here, we describe a section of a modular instrumen...

Fluorescent labelling of macromolecular samples, including using the green fluorescent protein (GFP), has revolutionised the field of bioimaging. The ongoing development of fluorescent proteins require a detailed understanding of the photophysics of the biochromophore, and how chemical derivatisation influences the excited state dynamics. Here, we...

The photophysics of biochromophore ions often depends on the isomeric or protomeric distribution, yet this distribution, and the individual isomer contributions to an action spectrum, can be difficult to quantify. Here, we use two separate photodissociation action spectroscopy instruments to record electronic spectra for protonated forms of the gre...

Polycyclic aromatic hydrocarbons have widely been conjectured to be ubiquitous in space, as supported by the recent discovery of two isomers of cyanonaphthalene, indene, and 2-cyanoindene in the Taurus molecular cloud-1 using radioastronomy. Here, the photoionization dynamics of 1-cyanonaphthalene (1-CNN) are investigated using synchrotron radiatio...

Several small Polycyclic Aromatic Hydrocarbons (PAHs) have been identified recently in the Taurus Molecular Cloud (TMC-1) using radio telescope observations. Reproducing the observed abundances of these molecules has been a challenge for astrochemical models. Rapid radiative cooling of PAHs by Recurrent Fluorescence (RF), the emission of optical ph...

Naphthalene and azulene are isomeric polycyclic aromatic hydrocarbons (PAHs) and are topical in the context of astrochemistry due to the recent discovery of substituted naphthalenes in the Taurus Molecular Cloud-1 (TMC-1). Here, the thermal-and photo-induced isomerization, dissociation, and radiative cooling dynamics of energized (vibrationally hot...

The green fluorescent protein (GFP) drove revolutionary progress in bioimaging. Photoconvertible fluorescent proteins (PCFPs) are an important branch of the FP family, of which Kaede is the prototype. Uniquely, PCFPs can be permanently switched from green to red emitting forms on UV irradiation, facilitating applications in site-specific photolabel...

Carbon aggregates containing between 10 and 30 atoms preferentially arrange themselves as planar rings. To learn more about this exotic allotrope of carbon, electronic spectra are measured for even cyclo[n]carbon radical cations (C14+-C36+) using two-color photodissociation action spectroscopy. To eliminate spectral contributions from other isomers...

After decades of searching, astronomers have recently identified specific Polycyclic Aromatic Hydrocarbons (PAHs) in space. Remarkably, the observed abundance of cyanonaphthalene (CNN, C10H7CN) in the Taurus Molecular Cloud (TMC-1) is six orders of magnitude higher than expected from astrophysical modeling. Here, we report unimolecular dissociation...

Fluorescence spectroscopy of gas-phase ions generated through electrospray ionization is an emerging technique able to probe intrinsic molecular photophysics directly without perturbations from solvent interactions. While there is ample scope for the ongoing development of gas-phase fluorescence techniques, the recent expansion into low-temperature...

The time-dependent photodetachment action spectra of the linear hydrocarbon anions C 4 H ⁻ and C 6 H ⁻ are investigated using the cryogenic electrostatic ion storage ring DESIREE. Radiative cooling characteristics of the ions on the millisecond to second timescale are probed by monitoring changes in the spectra as the ions cool by spontaneous infra...

Molecules based on the deprotonated p-hydroxycinnamate moiety are widespread in nature, including serving as UV filters in the leaves of plants and as the biochromophore in photoactive yellow protein. The photophysical behavior of these chromophores is centered around a rapid E → Z photoisomerization by passage through a conical intersection seam....

Electronic spectra are measured for protonated carbon clusters (C2n+1H+) containing between 7 and 21 carbon atoms. Linear and cyclic C2n+1H+ isomers are separated and selected using a drift tube ion mobility stage before being mass selected and introduced into a cryogenically cooled ion trap. Spectra are measured using a two-color resonance-enhance...

After decades of speculation and searching, astronomers have recently identified specific Polycyclic Aromatic Hydrocarbons (PAHs) in space. Remarkably, the observed abundance of cyanonaphthalene (CNN, C10H7CN) in the Taurus Molecular Cloud (TMC-1) is six orders of magnitude higher than expected from astrophysical modeling. Here, we report absolute...

The unimolecular dissociation and infrared radiative cooling rates of cationic 1-hydroxypyrene (OHPyr$^+$, \ce{C16H10O+}) and 1-bromopyrene (BrPyr$^+$, \ce{C16H9Br+}) are measured using a cryogenic electrostatic \rev{ion beam} storage ring. A novel numerical approach is developed to analyze the time dependence of the dissociation rate and to determ...

The diarylethene chromophore is commonly used in light-triggered molecular switches. The chromophore undergoes reversible 6π-electrocyclisation (ring closing) and cycloreversion (ring opening) reactions upon exposure to UV and visible light, respectively, providing bidirectional photoswitching. Here, we investigate the gas-phase photoisomerisation...

We report measurements of the statistical vibrational autodetachment (VAD, also called thermionic emission) and radiative cooling rates of isolated para-benzoquinone (pBQ, C6H4O2) radical anions using the cryogenic electrostatic ion storage ring facility DESIREE. The results are interpreted using master equation simulations with rate coefficients c...

Infrared and electronic spectra are indispensable for understanding the structural and energetic properties of charged molecules and clusters in the gas phase. However, the presence of isomers can potentially complicate the interpretation of spectra, even if the target molecules or clusters are mass-selected beforehand. Here, we describe an instrum...

The photoisomerization behavior of styryl 9M, a common dye used in material sciences, is investigated using tandem ion mobility spectrometry (IMS) coupled with laser spectroscopy. Styryl 9M has two alkene linkages, potentially allowing for four geometric isomers. IMS measurements demonstrate that at least three geometric isomers are generated using...

Electronic spectra are measured for mass-selected C2n⁺ (n=6-14) clusters over the visible and near infrared spectral range through resonance enhanced photodissociation of clusters tagged with N2 molecules in a cryogenic ion trap. The target C2n⁺ clusters are generated through laser ablation of a graphite disk, and can be selected according to their...

Incorporation of fluorescent proteins into biochemical systems has revolutionized the field of bioimaging. In a bottom-up approach, understanding the photophysics of fluorescent proteins requires detailed investigations of the light-absorbing chromophore, which can be achieved by studying the chromophore in isolation. This paper reports a photodiss...

The spectroscopy and photo-induced dissociation of flavin mononucleotide anions in vacuo are investigated over the 300–500 nm wavelength range. Comparison of the dependence of fragment ion yields as a function of deposited photon energy with calculated dissociation energies and collision-induced dissociation measurements performed under single-coll...

This roadmap article highlights recent advances, challenges and future prospects in studies of the dynamics of molecules and clusters in the gas phase. It comprises nineteen contributions by scientists with leading expertise in complementary experimental and theoretical techniques to probe the dynamics on timescales spanning twenty order of magnitu...

Superhydrogenated polycyclic aromatic hydrocarbons (PAHs) have been suggested to catalyze the formation of H 2 in certain regions of space, but it remains unclear under which circumstances this mechanism is viable given the reduced carbon backbone stability of superhydrogenated PAHs. We report a laboratory study on the stability of the smallest per...

Astrochemical modelling has proposed that 10% or more of interstellar carbon could be tied up as polycyclic aromatic hydrocarbon (PAH) molecules. Developing reliable models of the interstellar carbon lifecycle requires calibration data obtained through laboratory studies on relevant chemical and physical processes, including on the photo-induced an...

Luciferin molecules are common luminophores found throughout the biological kingdoms. Here, electrospray ionization and tandem ion mobility spectrometry coupled with laser spectroscopy are used to demonstrate that D-luciferin and oxyluciferin deprotonated anions can be produced in two isomeric forms, which can be separated by virtue of their differ...

Tandem ion mobility mass spectrometry-coupled laser excitation is used to record photodetachment, photoisomerization and photodepletion action spectra for a series of deprotomer-selected hydroxycinnamate anions, including deprotonated caffeic, ferulic and sinapinic acids. This molecular series accounts for most hydroxycinnamic moieties found in nat...

Time-resolved spontaneous and laser-induced unimolecular fragmentation of perylene cations (C 20 H 12 +) has been measured on timescales up to 2 s in a cryogenic electrostatic ion beam storage ring. We elaborate a quantitative model, which includes fragmentation in competition with radiative cooling via both vibrational and electronic (recurrent fl...

Dye molecules based on the xanthene unit are widely used as fluorescent probes in bioimaging and technological applications due to their large absorption cross-section for visible light and high fluorescence quantum yield. These applications require a clear understanding of the dye's inherent photophysics and the effect of a condensed-phase environ...

Radiative cooling of carbon cluster anions C 2n+1 ⁻ ( n = 3–5) is investigated using the cryogenic electrostatic ion storage ring DESIREE. Two different strategies are applied to infer infrared emission on slow (milliseconds to seconds) and ultraslow (seconds to minutes) timescales. Initial cooling of the ions over the millisecond timescale is prob...

Spectroscopic characterisations of the radical polyinterhalogen molecules IF2 and I2F are reported using anion photoelectron spectroscopy. The corresponding parent anions, IF2- and I2 F− , are common products formed in...

Non-valence states of neutral molecules (Rydberg states) play important roles in non-adiabatic dynamics of excited states. In anions, such non-adiabatic transitions between non-valence and valence states have been much less explored even though they are believed to play important roles in electron capture and excited state dynamics of anions. The a...

Chromophores based on the para-hydroxycinnamate moiety are widespread in the natural world, including as the photoswitching unit in photoactive yellow protein and as a sunscreen in the leaves of plants. Here, photodetachment action spectroscopy combined with frequency- and angle-resolved photoelectron imaging is used to fingerprint the excited stat...

Photoswitching of a charged azobenzene-stilbene dye is investigated through laser excitation in a tandem ion mobility mass spectrometer. Action spectra associated with E → Z and Z → E photoisomerisation of the stilbene group exhibit bands at 685 and 440 nm, corresponding to S1 ← S0 and S3 ← S0 transitions, respectively. The data suggest that isomer...

Indigoid chromophores have emerged as versatile molecular photoswitches, offering efficient reversible photoisomerization upon exposure to visible light. Here we report synthesis of a new class of permanently charged hemiindigos (HIs) and characterization of photochemical properties in gas phase and solution. Gas‐phase studies, which involve exposi...

Non-valence states in neutral molecules (Rydberg states) have well-established roles and importance in photochemistry, however, considerably less is known about the role of non-valence states in photo-induced processes in anions. Here, femtosecond time-resolved photoelectron imaging is used to show that photoexcitation of the S1(ππ*) state of the m...

Ultraslow radiative cooling lifetimes and adiabatic detachment energies for three astrochemically relevant anions, Cn− (n = 3–5), are measured using the Double ElectroStatic Ion Ring ExpEriment (DESIREE) infrastructure at Stockholm University. DESIREE maintains a background pressure of ≈10⁻¹⁴ mbar and temperature of ≈13 K, allowing storage of mass-...

Ultraslow radiative cooling lifetimes and adiabatic detachment energies for three astrochemically relevant anions, C$_n^-$ ($n=3-5$), are measured using the Double ElectroStatic Ion Ring ExpEriment (DESIREE) infrastructure at Stockholm University. DESIREE maintains a background pressure of $\approx$10$^{-14}$\,mbar and temperature of $\approx$13\,K...

The photoinduced excited state dynamics of gas-phase trans-retinoate (deprotonated trans-retinoic acid, trans-RA−) are studied using tandem ion mobility spectrometry coupled with laser spectroscopy, and frequency-, angle- and time-resolved photoelectron imaging. Photoexcitation of the bright S3(ππ*)  S0 transition leads to internal conversion to t...

Deprotonated para-coumaric acid is commonly considered as a model for the chromophore in photoactive yellow protein where it undergoes E→Z isomerization following absorption of blue light. Here, tandem ion mobility mass spectrometry is coupled with laser excitation to study the photochemistry of deprotonated para-coumaric acid, to show that the phe...

Substituted naphthalene anions (deprotonated 2-naphthol and 6-hydroxy-2-naphthoic acid) are spectroscopically probed in a tandem drift tube ion mobility spectrometer (IMS). Target anions are selected according to their drift speed through nitrogen buffer gas in the first IMS stage before being exposed to a pulse of tunable light that induces either...

Frequency-resolved (2D) photoelectron (PE) spectra of the anionic clusters (C6F6) n-, for n = 1-5, and time-resolved PE spectra of I-C6F6 are presented using a newly built instrument and supported by electronic structure calculations. From the 2D PE spectra, the vertical detachment energy (VDE) of C6F6- was measured to be 1.60 ± 0.01 eV, and the ad...

Substituted naphthalene anions (deprotonated 2-naphthol and 6-hydroxy-2-naphthoic acid) are spectroscopically probed in a tandem drift tube ion mobility spectrometer (IMS). Target anions are selected according to their drift speed through nitrogen buffer gas in the first IMS stage before being exposed to a pulse of tunable light that induces either...

The intrinsic optical properties and photochemistry of Flavin Adenine Dinucleotide (FAD) dianions are investigated using a combination of tandem ion mobility spectrometry and action spectroscopy. Two principal isomers are observed, the more stable form being deprotonated on the isoalloxazine group and a phosphate (N-3,PO4 deprotomer), and the other...

The shapes of many molecules can be transformed by light or heat. Here we investigate collision- and photon-induced interconversions of EE, EZ, and ZZ isomers of the isolated Congo red (CR) dianion, a double molecular switch containing two ─N═N─ azo groups, each of which can have the E or Z configuration. We find that collisional activation of CR d...

Fluorescent proteins have revolutionised the visualisation of biological processes, prompting efforts to understand and control their intrinsic photophysics. Here we investigate the photoisomerization of deprotonated p-hydroxybenzylidene-2,3-dimethylimidazolinone anion (HBDI⁻), the chromophore in green fluorescent protein and in Dronpa protein, whe...

Ruthenium sulfoxide complexes undergo thermally reversible linkage isomerization of sulfoxide ligands from S- to O-bound in response to light. Here, we report photoisomerization action spectra for a ruthenium bis-sulfoxide molecular photoswitch, [Ru(bpy)2(bpSO)]2+, providing the first direct evidence for photoisomerization of a transition metal com...

Separation and structural identification of lipids remain a major challenge for contemporary lipidomics. Regioisomeric lipids differing only in position(s) of unsaturation are often not differentiated by conventional liquid chromatography-mass spectrometry approaches leading to the incomplete, or sometimes incorrect, assignation of molecular struct...

Separation and structural identification of lipids remains a major challenge for contemporary lipidomics. Regioisomeric lipids differing only in position(s) of unsaturation are not differentiated by conventional liquid chromatography-mass spectrometry approaches leading to the incomplete, or sometimes incorrect, assignation of molecular structure....

Donor-acceptor Stenhouse adducts (DASAs) are a new class of photoswitching molecules with excellent fatigue resistance and synthetic tunability. Here, tandem ion mobility mass spectrometry coupled with laser excitation is used to characterize the photocyclization reaction of isolated, charge-tagged DASA molecules over the 450-580 nm range. The expe...

Substituted azobenzenes serve as chromophores and actuators in a wide range of molecular photoswitches. Here, tandem ion mobility spectrometry is coupled with laser excitation is used to investigate the photoisomerisation of selected E and Z isomers of the charge-tagged azobenzene, methyl orange. Both isomers display a weak S1(nπ*) photoisomerisati...

A detailed understanding of the dissociative electron ionization dynamics of SF6 is important in the modeling and tuning of dry-etching plasmas used in the semiconductor manufacture industry. This paper reports a crossed-beam electron ionization velocity-map imaging study on the dissociative ionization of cold SF6 molecules, providing complete, unb...

Frequency-resolved photoelectron spectroscopy applied to mass-selected cluster anions is an insightful approach to characterise the dynamics of π*-resonances with microsolvation. Here, the technique demonstrated with monomer, dimer and trimer radical anions of para-toluquinone (pTQ) over a ~1 eV excitation window above the detachment threshold. The...

Due to their high photoisomerization efficiencies, azobenzenes and their functionalized derivatives are used in a broad range of molecular photoswitches. Here, the photochemical properties of the trans isomers of protonated azobenzene (ABH⁺) and protonated 4-aminoazobenzene (NABH⁺) cations are investigated in the gas phase using a tandem ion mobili...

The utility of tandem ion mobility mass spectrometry coupled with electronic spectroscopy to investigate protomer-specific photochemistry is demonstrated by measuring the photoisomerization response for protomers of protonated 4-dicyanomethylene-2-methyl-6-para-dimethylaminostyryl-4H-pyran (DCM) molecules. The target DCMH⁺ species, has three protom...

We present the first experimental demonstration of Z↔E photoisomerization the GFP chromophore anion, HBDI⁻, in the gas phase. In the single photon absorption regime, the photoisomerization action spectra show two maxima at 480 nm and 455 nm. In the multiphoton absorption regime, photodissociation and photodetachment channels modify the appearance o...

The photoisomerisation of charged molecules in solution is probed directly using ion mobility mass spectrometry with electrospray ionisation. The technique is demonstrated using a prototype azoheteroarene cation in methanol. By scanning the wavelength of the excitation light while monitoring the photoisomer intensity one can generate a photoisomeri...

Nonvalence states of molecular anions play key roles in processes, such as electron mobility, in rare-gas liquids, radiation-induced damage to DNA, and the formation of anions in the interstellar medium. Recently, a class of nonvalence bound anion state has been predicted by theory in which correlation forces are predominantly responsible for bindi...

We report the first example of an alkene with two carbon-bound substituents (imidazole and imidazolium rings) where the Z-isomer has a greater thermodynamic stability than the E-isomer which persists in both the gas phase and in solution. Theoretical calculations, solution fluorescence spectroscopy and gas-phase ion mobility mass spectrometry studi...

We report the first example of an alkene with two carbon-bound substituents (imidazole and imidazolium rings) where the Z-isomer has a greater thermodynamic stability than the E-isomer which persists in both the gas phase and in solution. Theoretical calculations, solution fluorescence spectroscopy and gas-phase ion mobility mass spectrometry studi...

Photoisomerisation of protonated azobis(2-imidazole), an intramolecular hydrogen-bonded azoheteroarene photoswitch molecule, is investigated in the gas phase using tandem ion mobility mass spectrometry. The E and Z isomers exhibit distinct spectral responses, with E-Z photoisomerisation occurring over the 360--520 nm range (peak at 460 nm), and Z-E...

An ion mobility spectrometer (IMS) with an electrospray ion source is used to investigate photo and thermal isomerization of photoactive molecules in the electrospray syringe. A light emitting diode adjacent to the syringe establishes a photostationary state that relaxes thermally towards the more stable isomer once illumination ceases. The arrange...

Photoelectron spectroscopy of the deprotonated octatrienoic acid anion, [C7H9–CO2]⁻, shows the formation of [C7H9]⁻ and loss of H– at hν = 4.13 eV. Using velocity map imaging, the H– fragment was characterized to have a Boltzmann-like kinetic energy distribution consistent with dissociation on a ground electronic state. Similar dynamics were not ob...

The recently developed method of frequency-, angle-, and time-resolved photoelectron imaging (FAT-PI) applied to the study of the dynamics of resonances of open-shell anions is reviewed. The basic principles of the method and its experimental realisation are outlined. The dynamics of a number of radical quinone anions is then considered. Firstly, w...

The biological antioxidant activity of vitamin E has been related to the stability of the tocopheroxyl radical. Using anion photoelectron imaging and electronic structure calculations, the four tocopheroxyl components of vitamin E have been studied in the gas-phase and have yielded the adiabatic detachment energies of the α-, β/γ- and δ-tocopheroxy...

Isolated π-stacked dimer radical anions present the simplest model of an excess electron in a π-stacked environment. Here, frequency-, angle-, and time-resolved photoelectron imaging and electronic structure calculations have been used to characterise the π-stacked coenzyme Q0 dimer radical anion and its exited state dynamics. In the ground electro...

A photoelectron imaging study of the text-book antimony tartrate dianion is presented. The vertical and adiabatic detachment energies are determined to be 2.5 ± 0.1 eV and 2.1 ± 0.2 eV, respectively. The photoelectron spectra exhibit a typical cut-off due to the presence of the repulsive Coulomb barrier (RCB) and the photoelectron images are highly...

Photoelectron velocity-map imaging and electronic structure calculations have been used to study the temporary anion (resonance) dynamics of the closed-shell site-specific deprotonated tetracene anion (C18H11(-)) in the hv = 3.26 eV (380 nm) to 4.13 eV (300 nm) range. In accord with a recent frequency-, angle-, and time-resolved photoelectron imagi...

Temporary radical anions (resonances) of isolated coenzyme Q0 (CQ0) and their associated above-threshold dynamics have been studied using frequency-, angle-, and time-resolved photoelectron imaging (FAT-PI). Experimental energetics and dynamics are supported with ab initio calculations. All results support that CQ0 exhibits similar resonances and e...

A combined frequency-, angle-, and time-resolved photoelectron spectroscopy study is used to unravel the excited state dynamics following UV excitation of the isolated anionic chromophore of the green fluorescent protein (GFP). The optically-bright S3 state, which is populated for hv > 3.7 eV, is shown to decay predominantly by internal conversion...

This paper reports a crossed-beam velocity-map imaging study into the electron ionization dynamics of jet-cooled N 2 and O 2 molecules at electron collision energies from 35 to 100 eV. The use of velocity-map imaging detection provides insight into the detailed ionization dynamics through the dimension of the product ion kinetic energy associated w...

The photoelectron signal of the singly deprotonated fluorescein anion is found to be highly dependent on the relative polarization between pump and probe pulses, and time-resolved photodetachment anisotropy (TR-PA) is developed as a probe of the rotational dynamics of the chromophore. The total photoelectron signal shows both rotational and vibrati...

Frequency-, angle-, and time-resolved photoelectron imaging of gas-phase menadione (vitamin K3) radical anions is used to show that quasi-bound resonances of the anion can act as efficient doorway states to produce metastable ground electronic state anions on a sub-picosecond timescale. Several anion resonances have been experimentally observed and...

The resonant attachment of a free electron to a closed shell neutral molecule, and the interplay between the following electron detachment and electronic relaxation channels represents a fundamental but common process throughout chemical and biochemical systems. The new methodology of anion frequency-resolved photoelectron imaging is detailed and u...

This account introduces a new variant of time-of-flight mass spectrometry, termed velocity-map imaging mass spectrometry (VMImMS). While the ion abundances recorded in conventional ToF-MS measurements are highly useful for molecular quantification and structure determination, the final parent and fragment ion yields are Largely blind to the dynamic...

Accurate ionization cross-sections for DNA and RNA constituents in the condensed or aqueous phase are important parameters for models simulating radiation damage to genetic material in living cells. In this work, absolute gas-phase electron total ionization cross-sections (TICSs) have been measured for a series of six aromatic and eight non-aromati...

Perfluorocarbons (PFCs) are man-made compounds whose ion physics exhibit complex interplays between statistical and nonstatistical fragmentation and intramolecular rearrangement processes. One probe of such processes is the energy-dependent electron-impact-ionization cross section. Partial electron-impact-ionization cross sections are reported for...

By integrating a velocity-map imaging lens and position sensitive detector into an electron-impact time-of-flight mass spectrometer, it becomes possible to record ion kinetic energy release (KER) distributions for each fragment ion alongside the time-of-flight mass spectrum. The KER distributions allow ions of identical mass-to-charge ratio to be d...

This paper describes single-crystal measurements on a crystal plate cut from a naturally-occurring almandine-rich single crystal (Alm 69Pyr 19Spe 8Gro 4) from Wrangell Alaska. The objective was to measure the mean-squared-displacement (msd) tensor precisely using Mössbauer spectroscopy. Parallel quantum-mechanical calculations based on X-ray determ...

The experimental determination of absolute total electron impact ionization cross-sections for polyatomic molecules has traditionally been a difficult task and restricted to a small range of species. This article reviews the performance of three models to estimate the maximum ionization cross-sections of some 65 polyatomic organic and halocarbon sp...

Since the pioneering work on the theoretical description of Mössbauer quadrupole line intensities for a single-crystal to elucidate information on the electric-field-gradient (EFG) tensor, ferrous chloride tetrahydrate, FeCl(2)·4H(2)O, has represented a prototypical Mössbauer species. In addition, this species also typifies a so-called ambiguous, l...

This paper outlines the discovery of a newly characterised isomorph of ferrous chloride tetrahydrate, Fe(H2O)6·FeCl4(H2O)2, which was initially identified by X-ray crystallography and confirmed by Mössbauer spectroscopy. The X-ray analysis identified the space group as P21/c with essentially the same unit cell dimensions as the well-known isomorph,...

This paper reports the determination of the electric-field-gradient and mean-squared-displacement tensors in 57Fe symmetry-related sites of 1̄ Laue class in monoclinic FeCl2. 4H2O at room temperature by single-crystal Mössbauer spectroscopy. Contrary to all previous work, the mean-squared-displacement matrix (tensor), , is not constrained to be iso...