Damian Kokkin

Marquette University · Department of Chemistry

The anisole-ammonia 1:1 complex is a challenge for both experiment and theory. Early studies supported a non-planar structure, involving a trifecta of weak non-covalent interactions: N-H/O, N-H/π, and C-H/N. The calculated structure and binding energy of the complex proved remarkably sensitive to the level of theory employed. Here, we report the fi...

Recent studies of the weakly bound anisole⋯CH4 complex found a dual mode of binding, featuring both C/H⋯π and C/H⋯O noncovalent interactions. In this work, we examine the dissociation energies of related aniline⋯(CH4)n (n = 1, 2) van der Waals clusters, where both C/H⋯π and C/H⋯N interactions are possible. Using a combination of theory and experime...

The 3-ethynylcyclopentenyl radical (3ecpr) has been identified as the carrier of an electronic spectrum with origin at 21,792 cm⁻¹ using resonant ionization and laser-induced fluorescence spectroscopies. The radical was first detected in a toluene discharge and is most efficiently produced from 1,6-heptadiyne. Overwhelming spectroscopic and chemica...

Non-covalent forces such as hydrogen bonding, halogen bonding, π-π stacking, C-H/π and C-H/O interactions hold the key to such chemical processes as protein folding, molecular self-assembly, and drug-substrate interactions. Invaluable insight into the nature and strength of these forces continues to come from the study of isolated molecular cluster...

Studies of exciton and hole stabilization in multichromophoric systems underpin our understanding of electron transfer and transport in materials and biomolecules. The simplest model systems are dimeric, and recently we compared the gas-phase spectroscopy and dynamics of van der Waals dimers of fluorene, 9-methylfluorene (MF), and 9,9′-dimethylfluo...

Efficient exciton and charge delocalization across π‐stacked assemblies is of critical importance in biological systems and functional polymeric materials. To examine the requirements for exciton and hole stabilization, we report the design, synthesis, and characterization of a novel set of cofacial bifluorene (F2) torsionomers: unhindered (model)...

Efficient exciton and charge delocalization across π‐stacked assemblies is of critical importance in biological systems and functional polymeric materials. To examine the requirements for exciton and hole stabilization, we report the design, synthesis, and characterization of a novel set of cofacial bifluorene (F2) torsionomers: unhindered (model)...

π -stacking interactions are ubiquitious across chemistry and biochemistry, impacting areas from organic materials and photovoltaics to biochemistry and DNA. However, experimental data is lacking re-garding the strength of π-stacking forces - an issue not settled even for the simplest model system, the isolated benzene dimer. Here, we use 2-color a...

The products of an electrical discharge containing toluene are interrogated using resonance-enhanced multiphoton ionization and laser-induced fluorescence spectroscopies. A previously unreported electronic spectrum recorded at m/z = 105, with a putative origin band at 26053 cm⁻¹, is assigned to methyltropyl radical, which appears to be a major prod...

The [18.28]0⁻–a3Δ1 (0,0) band near 647 nm of tantalum nitride, TaN, has been recorded and analyzed field-free and in the presence of static electric and magnetic fields. The fine and hyperfine parameters for the a3Δ1 and [18.28]0⁻ states are determined. The ¹⁸¹Ta(I = 7/2) axial nuclear electric quadrupole coupling constant, eQq0, and the effective...

Understanding geometrical and size dependencies of through-space charge delocalization in multichromophoric systems is critical to model electron transfer and transport in materials and biomolecules. In this work, we examine the size evolution of hole delocalization in van der Waals clusters of fluorene (i.e., (F)n), where a range of geometries are...

Excimer formation and charge resonance stabilization in covalently linked bichromophoric systems with flexible spacers are important processes relevant to biochemistry and functional materials. Requiring a π-stacked cofacial arrangement of a pair of aromatic molecules at a van der Waals contact, the underlying geometrical reorganization that accomp...

High resolution laser-induced fluorescence (LIF) spectra of the [18.42]0⁺ − X¹Σ⁺ (0,0) band of tantalum nitride, TaN, near 543 nm, have been recorded and analyzed field-free and in the presence of a static electric field. The nuclear electric quadrupole hyperfine structure due to ¹⁸¹Ta(I=7/2) was resolved and analysis of the field-free spectrum yie...

The dispersed fluorescence following pulsed dye laser excitation of the $\textrm{B}_2 \Sigma^+ - \textrm{X}^2 \Sigma^+(0,0)$ band of a cold sample of SiO$^+$ has been recorded and analyzed. The branching ratios for $\textrm{B}_2 \Sigma^+ (v=0) \rightarrow \textrm{X}^2 \Sigma^+(v)$ and $\textrm{B}_2 \Sigma^+ (v=0) \rightarrow \textrm{A}^2 \Pi_i(v)$...

Singly deuterated silylene has been detected and characterized in the gas-phase using high-resolution, two-dimensional, optical spectroscopy. Rotationally resolved lines in the 000X̃1A′→Ã1A″ band are assigned to both c-type perpendicular transition and additional parallel, axis-switching induced bands. The extracted rotational constants were combin...

The dispersed laser induced fluorescence resulting from excitation in the regions of the [17.58]0+− (0,0), [18.42]0+− (0,0), [19.22]1− (0,0), and [19.40]1− (0,0) bands of tantalum nitride, 181TaN, have been recorded and analyzed. The branching ratios and radiative lifetimes for the [17.58]0+ (v=0), [18.42]0+(v=0), [19.22]1+(v=0), and [19.40]1(v=0)...

This paper provides spectral characterization of the two isomers of the 1-methylenepyrene cation namely the 1-pyrenemethylium and a pyrene-like isomer owing a tropylium cycle. Both are possible photodissociation products of the 1-methylpyrene cation and were proposed as potential contributors to the Diffuse Interstellar Bands. In that respect, vibr...

Gold monosulfide, AuS, has been detected and characterized in the gas phase using optical spectroscopy. The symmetries of the ground and low-lying electronic excited states have been determined by application of a synergy of hot and cold laser excitation techniques. The electronic spectra are assigned to progressions in four band systems associated...

Thorium dimer, Th2, has been detected in the gas phase via two dimensional laser induced fluorescence electronic spectroscopy. The visible excitation spectra are broad, unstructured features with an approximate linewidth of 10 cm-1. The spectrum consists of vibrational progressions associated with excitation from the ground electronic state to two...

The magnetic tuning of the low rotational levels in the (v = 0) X2Σ+, (v = 0) A2Π, and (v = 0) B2Σ+ electronic states of calcium monofluoride, CaF, have been experimentally investigated using high resolution optical Zeeman spectroscopy of a cold molecular beam. The observed Zeeman shifts and splittings are successfully modeled using a traditional e...

We report the gas-phase optical detection of Si2C near 390 nm and the first experimental investigation of the rovibrational structure of its 1A1 ground electronic state using mass-resolved and fluorescence spectroscopy and variational calculations performed on a high-level ab initio potential. From this joint study, it is possible to assign all ob...

The I(|Ω|=1)–X1Σ+(0,0) band near 512 nm of thorium oxide has been recorded and analyzed field free and in the presence of both static electric and magnetic fields. The determined T00, B, and q field-free parameters for the I(|Ω|=1)(v=0) state are (incm−1)19539.3823±0.0003,0.328 69±0.000 03, and 0.001 54 ± 0.000 05. The Zeeman-induced shifts and spl...

The electronic spectrum of Si3C has been measured in the 710-250 nm region by resonant two-color two-photon ionization spectroscopy. In addition to the strong A1 transition near 400 nm, evidence is found for two weaker features: a broad, largely structureless band near 625 nm, which is assigned to A1, and a band near 333 nm with partially-resolved...

The dispersed laser induced fluorescence resulting from excitation of the U(|Ω|=1)−X1Σ+(0,0), L(|Ω|=1)−X1Σ+(0,0), and I(|Ω|=1)−X1Σ+(0,0) bands near 398, 402, and 512 nm, respectively, of thorium oxide, ThO, has been recorded and analyzed. The branching ratios for the fluorescence decay from the U(|Ω|=1)(v=0), L(|Ω|=1)(v=0), and I(|Ω|=1)(v=0) states...

Polycyclic aromatic hydrocarbons (PAHs) are key species encountered in a large variety of environments such as the Interstellar Medium (ISM) and in combustion media. Their UV spectroscopy and photodynamics in neutral and cationic forms are important to investigate in order to learn about their structure, formation mechanisms, and reactivity. Here,...

The optical Stark effect in numerous low-J branch features in the Omega = 0(+) <- X-3 Sigma(-)(0) band near 19 040 cm(-1) of nickel oxide, NiO, has been recorded and analyzed. The permanent electric dipole moment, (mu) over bar (el), for the X-3 Sigma(-)(0)(v = 0) and [19.04] Omega = 0(+) states were determined to be 4.43 +/- 0.04 D and 1.85 +/- 0....

The gas-phase optical spectra of three silicon-terminated carbon chain radicals, SiCnH (n = 3 - 5), formed in a jet-cooled discharge of silane and acetylene, have been investigated by resonant two-color two-photon ionization and laser-induced fluorescence/dispersed fluorescence. Analysis of the spectra was facilitated by calculations performed usin...

Cationic polycyclic aromatic hydrocarbons (PAHs) are attractive candidates for the Diffuse Interstellar Bands, but to date not a single PAH species has been identified on the basis of a spectral agreement. This indicates either that the molecular diversity is very large or that the candidates that have been considered are not the correct ones. In p...

The state-dependent spectroscopy of α-methylbenzyl radical (α-MeBz) has been studied under jet-cooled conditions. Two-color resonant two-photon ionization (2C-R2PI), laser-induced fluorescence, and dispersed fluorescence spectra were obtained for the D0-D1 electronic transition of this prototypical resonance-stabilized radical in which the methyl g...

Threshold Photoelectron spectra (TPES), as well as Total Ion Yeld (TIY) spectra of jet-cooled Coronene (C_{12}H_{24}) have been obtained using the electron/ion coincidence imaging spectrometer DELICIOUS II available at the DESIRS beamline of the French Synchrotron facility SOLEIL. The obtained data can be interpreted in the light of new theoretical...

Polycyclic aromatic hydrocarbon (PAH) clusters have been proposed as candidates for evaporating very small grains that are revealed by their mid-IR emission at the surface of UV-irradiated clouds in interstellar space. This motivates studies on the photostability and spectroscopic signatures of such species to validate their presence in interstella...

Combustion processes involve a myriad of complex reaction pathways which connect smaller precursors to larger polyaromatic hydrocarbons, many of which are still unknown. In particular, benzyl-type radicals play an important role in combustible fuels due to their intrinsic resonance stabilization and consequent increase in relative concentration. He...

Though it has yet to be detected in space, there is good reason to believe that the disilicon carbide molecule, Si_2C, is an abundant constituent of circumstellar shells such as IRC+10216, in which the isovalent ionic ring SiC_2 is highly conspicuous. Si_2C exhibits a surprisingly complicated R2C2PI spectrum, which EOM-CCSD calculations indicate ar...

The gas phase optical spectra of the silicon terminated carbon chains, SiC_nH (n=3-5) formed in a silane acetylene discharge, have been investigated by R2C2PI and LIF/DF and will be reported here for the first time. Complementary to the experimental work, a theoretical investigation was undertaken with coupled cluster methods to garner a comprehens...

Polycyclic aromatic hydrocarbons (PAHs) and their cations are considered as attractive candidates for the Diffuse Interstellar Bands, some discrete absorption features observed throughout the visible and near-infrared spectral range whose origin is still investigated. So far, not a single PAH species has been identified on the basis of a spectral a...

We report the measurement of a jet-cooled electronic spectrum of the silicon trimer. Si(3) was produced in a pulsed discharge of silane in argon, and the excitation spectrum examined in the 18 000-20 800 cm(-1) region. A combination of resonant two-color two-photon ionization (R2C2PI) time-of-flight mass spectroscopy, laser-induced fluorescence/dis...

The molecular structure of trans, planar hydridotrioxygen (HOOO) has been examined by means of isotopic spectroscopy using Fourier transform microwave as well as microwave-millimeter-wave double resonance techniques, and high-level coupled cluster quantum-chemical calculations. Although this weakly bound molecule is readily observed in an electrica...

Following the initial detection of the C_2 Swan origin bands in the Red Rectangle, an unusual biconical protoplanetary nebula, a concerted effort has been undertaken in understanding this key astrophysical molecule from both the theoretical and experimental standpoint. In this talk we will present integral field observations on the Red Rectangle pa...

Following the initial detection of the C$_2$ Swan origin bands in the Red Rectangle, an unusual biconical protoplanetary nebula, a concerted effort has been undertaken in understanding this key astrophysical molecule from both the theoretical and experimental standpoint. In this talk we will present integral field observations on the Red Rectangle...

The rotational spectra of {sup 29}SiC{sub 2} and {sup 30}SiC{sub 2}, two silicon isotopic species of the abundant astronomical ring {sup 28}SiC{sub 2}, have been characterized in the millimeter band between 140 and 360 GHz in a low pressure discharge through SiH{sub 4}, C{sub 2}H{sub 2}, and Ar. Precise rotational and centrifugal distortion constan...

The rotational spectra of 29SiC2 and 30SiC2, two silicon isotopic species of the abundant astronomical ring 28SiC2, have been characterized in the millimeter band between 140 and 360 GHz in a low pressure discharge through SiH4, C2H2, and Ar. Precise rotational and centrifugal distortion constants have been derived for both species by fitting a sta...

Electronic spectra of CuSH (lower trace) and CuSD (upper trace), formed in a jet-cooled discharge of dihydrogen sulfide diluted in argon, struck between copper electrodes. The jet-cooled electronic spectrum of CuSH and CuSD near 430nm has been measured. An efficient method for producing metal hydrosulfides in the gas-phase is suggested. Calculation...

We report the first recording of the visible spectrum of gas-phase Si_3. A cold molecular beam sample was produced by skimming the output of a pulsed discharge source. The 545-490 nm spectral region was examined using both mass-selected REMPI and pulsed dye laser excitation with LIF detection. Dispersed fluorescence and lifetime measurements of num...

Polycyclic aromatic hydrocarbons are a class of molecules of broad interest that has long been explored by various spectroscopic techniques. The electronic spectroscopy of these species is of particular interest since it provides a framework for the understanding of the electronic structure of large polyatomic molecules. Such studies also allow the...

The optical spectra of the atomic clusters Si_3 and S_3 will be discussed in detail. The jet-cooled 2-colour resonant-2-photon ionisation spectrum of Si_3 has now been detected for the first time in the 530 nm region. For Si_3 a progression in the excited state bending and stretching modes are seen built onto the origin. Lower state frequencies der...

We report the first measurement of an electronic spectrum of Si_2C, observed in a jet-cooled discharge through silane, acetylene and argon, in the 380-410 nm wavelength range. While Si_2C is a highly plausible astronomical molecule, searches for its rotational transitions in the laboratory and in space are impractical at present - ab initio predict...

A protocol is developed for the identification of discharge intermediates from complex electronic spectra. The protocol involves resonant ionisation mass spectrometry to determine the mass of the unknown carrier followed by a two-dimensional fluorescence spectrum which is used as a "map" to guide higher resolution techniques. High resolution disper...

Until this work, the rotational spectra of the silicon isotopic species of SiCC were based almost entirely on astronomical frequencies, because only the fundamental 1_{0,1} - 0_{0,0} transition ^{29}SiC_2 and ^{30}SiC_2 had been measured in the laboratory. We have now derived precise rotational and centrifugal distortion constants from laboratory m...

The recent discovery and mapping of S_2 and SO_2 in the plume of Pele, one of the largest and most active volcanoes on Io, the innermost moon of Jupiter, suggests that other sulfur rich molecules may be abundant in this unusual planetary source. Optical images of Io in the range 3900 Å - 5000 Å conclude as much: the observed flux intensity cannot b...

Until this work, the rotational spectra of the silicon isotopic species of SiCC were based almost entirely on astronomical frequencies, because only the fundamental $1_{0,1} - 0_{0,0}$ transition $^{29}$SiC$_2$ and $^{30}$SiC$_2$ had been measured in the laboratory. {\bf 342}, L103 (1989)} We have now derived precise rotational and centrifugal dist...

The first optical spectrum of an isolated polycyclic aromatic hydrocarbon large enough to survive the photophysical conditions of the interstellar medium is reported. Vibronic bands of the first electronic transition of the all-benzenoid polycyclic aromatic hydrocarbon hexa-peri-hexabenzocoronene were observed in the 4080-4530 Å range by resonant 2...

The gas-phase laser-induced fluorescence (LIF) spectrum of a 1-phenylpropargyl radical has been identified in the region 20,800-22,000 cm(-1) in a free jet. The radical was produced from discharges of hydrocarbons including benzene. Disregarding C2, C3, and CH, this radical appears as the most strongly fluorescing product in a visible wavelength tw...

The jet-cooled laser-induced fluorescence and dispersed fluorescence spectra of the $ S_1(A_1') \leftarrow S_0(A_1')$ transition of triphenylene are reported. The spectra exhibit false origins of $e'$ symmetry which are modelled by performing calculations of Herzberg-Teller coupling using time-dependent density functional theory. It is found that t...

In order to produce laboratory analogues of the carbonaceous cosmic dust, a new chemical reactor has been built at the Laboratoire de Photophysique Moleculaire in Orsay, France. A low pressure flat burner provides flames of premixed hydrocarbon/oxygen gas mixtures, closely following the model system used by the combustion community. The flame is a...

A two-dimensional fluorescence (excitation/emission) spectrum of C2 produced in an acetylene discharge was used to identify and separate emission bands from the d (3)Pi(g)<--c (3)Sigma(u) (+) and d (3)Pi(g)<--a (3)Pi(u) excitations. Rotationally resolved excitation spectra of the (4<--1), (5<--1), (5<--2), and (7<--3) bands in the d (3)Pi(g)<--c (3...

High level ab initio calculations, using multireference configuration interaction (MRCI) techniques, have been carried out to investigate the spectroscopic properties of the singlet A 1Πu←X 1Σg+ Phillips, the triplet d 3Πg←a 3Σu Swan, the b 3Σg−←a 3Πu Ballik-Ramsay, and the d 3Πg←c 3Σu+ transitions of C2. The MRCI expansions are based on full-valen...

The jet-cooled laser-induced fluorescence and dispersed fluorescence spectra of the S1(A1')<--S0(A1') transition of triphenylene are reported. The spectra exhibit false origins of e' symmetry which are modeled by performing calculations of Herzberg-Teller coupling using time-dependent density functional theory. It is found that this level of theory...

Related to the problem of the diffuse interstellar bands (DIBs) is the unknown identity of the carriers of emission lines in the Red Rectangle, a nearby proto-planetary nebula, known as the Red Rectangle Bands (RRBs). We have used integral field spectroscopy with the 8m VLT (and 4m AAT) to spatially map the spectra of the RRBs and C2 Swan Bands in...

One of the oldest mysteries in molecular spectroscopy is the identity of the carriers of the diffuse interstellar bands (DIBs). Related to this problem is the unknown identity of the carriers of emission lines in the Red Rectangle, a nearby proto-planetary nebula, known as the Red Rectangle Bands (RRBs). Our strategy to uncover the carriers of the...

The $d^{3}\Pi_{g}-c^{3}\Sigma_{u}^{+}$ system of dicarbon was observed in a discharged supersonic jet of C$_2$H$_2$.}, \textit{J. Chem. Phys.} \underline{\textbf{125}}, 231101 (2006).} A spectral survey was carried out based on the result of high-level \textit{ab initio} calculation.}, \textit{J. Chem. Phys.} \underline{\textbf{126}}, 084302 (2007)...

A new band system of C(2), d (3)Pi(g)<--c (3)Sigma(u) (+) is observed by laser induced fluorescence spectroscopy, constituting the first direct detection of the c (3)Sigma(u) (+) state of C(2). Observations were made by laser excitation of c (3)Sigma(u) (+)(v(")=0) C(2), produced in an acetylene discharge, to the d (3)Pi(g)(v(')=3) level, followed...

The electronic excited-state properties of a series of dehydrogenated polycyclic aromatic hydrocarbons from phenyl through to decacyl are reported. The radicals were investigated by use of time-dependent density functional theory in conjunction with the B3LYP functional. The pi and n orbitals were seen to converge in energy as the system increased...

We have applied the tools of laser induced fluorescence and dispersed fluorescence to the products of a benzene discharge in a free jet with a view to identifying new hydrocarbon radicals. We have observed several new band systems in the visible and UV regions, including a putative origin at 4759\AA (air) which fluoresces to a ground state exhibiti...

High level \textit{ab initio} calculations were carried out on the $X^1\Sigma^+_g$, $A^1\Pi_u$, $a^3\Pi_u$, $b^3\Sigma^-_g$, $c^3\Sigma^+_u$ and $d^3\Pi_g$ levels of the C$_2$ radical. Calculations were carried out at the MRCI level with full-valence CASSCF reference wavefunctions and basis sets up to aug-cc-pv6z. The resulting wavefunctions and po...