Ralf I Kaiser

Ralf I Kaiser
University of Hawaiʻi at Mānoa | UH Manoa · Department of Chemistry

Professor
Looking for postdoctoral fellows in Reaction Dynamics and Material Sciences

About

681
Publications
58,563
Reads
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15,119
Citations
Citations since 2017
236 Research Items
7767 Citations
201720182019202020212022202305001,0001,500
201720182019202020212022202305001,0001,500
201720182019202020212022202305001,0001,500
201720182019202020212022202305001,0001,500

Publications

Publications (681)
Article
The gas-phase reaction between the 1-indenyl (C9H7•) radical and the cyclopentadienyl (C5H5•) radical has been investigated for the first time using synchrotron-based mass spectrometry coupled with a pyrolytic reactor. Soft photoionization with tunable vacuum ultraviolet photons afforded for the isomer-selective identification of the production of...
Article
Glycinal (HCOCH2NH2) and acetamide (CH3CONH2) are simple molecular building blocks of biomolecules in prebiotic chemistry, though their origin on early Earth and formation in interstellar media remain a mystery. These molecules are formed with their tautomers in low temperature interstellar model ices upon interaction with simulated galactic cosmic...
Article
Glycinal (HCOCH2NH2) and acetamide (CH3CONH2) are simple molecular building blocks of biomolecules in prebiotic chemistry, though their origin on early Earth and formation in interstellar media remain a mystery. These molecules are formed with their tautomers in low temperature interstellar model ices upon interaction with simulated galactic cosmic...
Article
1-Germavinylidene (H2CGe; X1A1), the germanium analogue of vinylidene (H2CC; X1A1), was prepared via a directed gas-phase synthesis through the bimolecular reaction of ground state atomic carbon (C; 3P) with germane (GeH4; X1A1) under single-collision conditions. The reaction commences with the barrierless insertion of carbon into the Ge-H bond fol...
Article
Full-text available
The formation of complex organic molecules by simulated secondary electrons generated in the track of galactic cosmic rays was investigated in interstellar ice analogs composed of methanol and carbon dioxide. The processed ices were subjected to temperature-programmed desorption to mimic the transition of a cold molecular cloud to a warmer star-for...
Article
Hypergolic ionic liquids have come under increased study for having several desirable properties as a fuel source. One particular ionic liquid, 1-ethyl-3-methylimidazolium/cyanoborohydride (EMIM+/CBH-), and oxidant, nitric acid (HNO3), has been reported to be hypergolic experimentally, but its mechanism is not well-understood at a mechanistic level...
Article
Since the observation of the first sulfur-containing molecule, carbon monosulfide (CS), in the interstellar medium (ISM) half a century ago, sulfur-bearing species have attracted great attention from the astrochemistry, astrobiology, and planetary geology communities. Nevertheless, it is still not clear in which forms most of the sulfur resides in...
Article
The simplest polycyclic aromatic hydrocarbon (PAH) carrying a five‐membered ring ‐ 9H‐fluorene (C13H10) ‐ is produced isomer‐specifically in the gas phase by reacting benzyl (C7H7•) with phenyl (C6H5•) radicals in a pyrolytic reac­tor coupled with single photon ionization mass spectrometry. The unconventional mechanism of reaction is supported by t...
Article
The simplest polycyclic aromatic hydrocarbon (PAH) carrying a five‐membered ring ‐ 9H‐fluorene (C13H10) ‐ is produced isomer‐specifically in the gas phase by reacting benzyl (C7H7•) with phenyl (C6H5•) radicals in a pyrolytic reac­tor coupled with single photon ionization mass spectrometry. The unconventional mechanism of reaction is supported by t...
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Full-text available
Carbonyl-bearing complex organic molecules (COMs) in the interstellar medium (ISM) are of significant importance due to their role as potential precursors to biomolecules. Simple aldehydes and ketones like acetaldehyde, acetone, and propanal have been recognized as fundamental molecular building blocks and tracers of chemical processes involved in...
Article
Although methanediamine (CH2(NH2)2) has historically been the subject of theoretical scrutiny, it has never been isolated to date. Here, we report the preparation of methanediamine (CH2(NH2)2)-the simplest diamine. Low-temperature interstellar analog ices composed of ammonia and methylamine were exposed to energetic electrons which act as proxies f...
Article
Gas-phase 1,3,5,7-cyclooctatetraene (C8H8) and triplet aromatic 1,3,5,7-cyclooctatetraene (C8H8) were formed for the first time through bimolecular methylidyne radical (CH)-1,3,5-cycloheptatriene (C7H8) reactions under single-collision conditions on a doublet surface. The reaction involves methylidyne radical addition to the olefinic π electron sys...
Article
1,1-Diamino-2,2-dinitroethene (FOX-7) is an energetic material with low sensitivity and high detonation performance, thus it has been considered as a potential replacement for traditional nitro-based energetic materials. In a recent publication (J. Phys. Chem. A, 2022, 126, 4747), the initial decomposition steps of FOX-7 were studied using reflectr...
Article
The gas-phase bimolecular reaction of the methylidyne (CH; X2Π) radical with vinylacetylene (H2CCHCCH; X1A') was conducted at a collision energy of 20.3 kJ mol-1 under single collision conditions exploiting the crossed molecular beam experimental results merged with ab initio electronic structure calculations and ab initio molecular dynamics (AIMD)...
Article
We unravel, for the very first time, the formation pathways of hydroxyacetone (CH3COCH2OH), methyl acetate (CH3COOCH3), and 3-hydroxypropanal (HCOCH2CH2OH), as well as their enol tautomers within mixed ices of methanol (CH3OH) and acetaldehyde (CH3CHO) analogous to interstellar ices in the ISM exposed to ionizing radiation at ultralow temperatures...
Article
For more than half a century, networks of radiative association, dissociative recombination, and bimolecular reactions have been postulated to drive the low-temperature chemistry of cold molecular clouds. Third-body stabilizations of collision complexes have been assumed to be ‘irrelevant’ due to short lifetime of such complexes. Here, we conduct c...
Article
Titanium (Ti), aluminum (Al), and boron (B) reactive mixed-metal nanopowders (Ti-Al-B RMNPs) represent attractive additives to hydrocarbon fuels such as exo-tetrahydrodicyclopentadiene (C10H16; JP-10) enhancing the limited volumetric energy densities of traditional hydrocarbons, but fundamental mechanisms and combustion stages in the oxidation have...
Article
We report the formation of the cyclic methylphosphonic acid trimer [c‐(CH3PO2)3] through condensation reactions during thermal processing of low‐temperature methylphosphonic acid samples exploiting photoionization reflectron time‐of‐flight mass spectrometry (PI−ReTOF−MS) along with electronic structure calculations. Cyclic methylphosphonic acid tri...
Article
The mechanism and chemical dynamics of the reaction of ground electronic state atomic carbon C(3Pj) with cyclopropane c-C3H6 (X1A1ʹ) have been explored by combining crossed molecular beams experiments with electronic...
Article
The molecular origins of homochirality on Earth is not understood well, particularly how enantiomerically enriched molecules of astrobiological significance like sugars and amino acids might have been synthesized on icy grains in space preceding their delivery to Earth. Polycyclic aromatic hydrocarbons (PAHs) identified in carbonaceous chondrites c...
Article
We investigated the photodissociation dynamics of three xylene isomers C6H4(CH3)2 at 157 nm. The center-of-mass translational energy distributions of C7H7 radicals were found to peak at 26 kJ mol⁻¹. Although the ionization energy of the C7H7 tolyl fragment exceeds the energy of a 157 nm photon, C7H7⁺ was observed as a result of the photoionization...
Article
The photodissociation dynamics of astrophysically relevant propyl derivatives (C3H7X; X = CN, OH, HCO) at 157 nm exploiting an ultracompact velocity map imaging (UVMIS) setup has been reported. The successful operation of UVMIS allowed the exploration of the 157 nm photodissociation of six (iso)propyl systems─n/i-propyl cyanide (C3H7CN), n/i-propyl...
Article
Silicon monoxide (SiO) is classified as a key precursor and fundamental molecular building block to interstellar silicate nanoparticles, which play an essential role in the synthesis of molecular building blocks connected to the Origins of Life. In the cold interstellar medium, silicon monoxide is of critical importance in initiating a series of el...
Article
Unravelling the generation of complex organic molecules (COMs) on interstellar nanoparticles (grains) is essential in establishing predictive astrochemical reaction networks and recognizing evolution stages of molecular clouds and star-forming regions. The formation of COMs has been associated with the irradiation of interstellar ices by ultraviole...
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Full-text available
We report the detection of fulvenallene ( c -C 5 H 4 CCH 2 ) in the direction of TMC-1 with the QUIJOTE ¹ line survey. Thirty rotational transitions with K a = 0,1,2,3 and J = 9−15 were detected. The best rotational temperature fitting of the data is 9 K and a derived column density is (2.7 ± 0.3) × 10 ¹² cm ⁻² , which is only a factor of 4.4 below...
Preprint
We report the detection of fulvenallene ($c$-C$_5$H$_4$CCH$_2$) in the direction of TMC-1 with the QUIJOTE line survey. Thirty rotational transitions with $K_a$=0,1,2,3 and $J$=9-15 were detected. The best rotational temperature fitting of the data is 9\,K and a derived column density is (2.7$\pm$0.3)$\times$10$^{12}$ cm$^{-2}$, which is only a fac...
Article
For more than half a century, pericyclic reactions have played an important role in advancing our fundamental understanding of cycloadditions, sigmatropic shifts, group transfer reactions, and electrocyclization reactions. However, the fundamental mechanisms of photochemically activated cheletropic reactions have remained contentious. Here we repor...
Article
Full-text available
We present the results of a spectral-line survey of the W51e1/e2 star-forming region at 68–88 GHz. 79 molecules and their isotopologues were detected, from simple diatomic or triatomic molecules, such as SO, SiO, and CCH, to complex organic compounds, such as CH 3 OCH 3 or CH 3 COCH 3 . A number of lines that are absent from the Lovas list of molec...
Preprint
We present the results of a spectral-line survey of the W51e1/e2 star-forming region at 68-88 GHz. 79 molecules and their isotopologues were detected, from simple diatomic or triatomic molecules, such as SO, SiO, and CCH, to complex organic compounds, such as CH$_3$OCH$_3$ or CH$_3$COCH$_3$. A number of lines that are absent from the Lovas list of...
Article
The tetrahedral 1,2,3-triphospha-4-azatricyclo [1.1.0.02,4] butane (P3N) molecule-an isovalent species of phosphorus (P4)-was prepared in low-temperature (5 K) phosphine-nitrogen ices and was identified in the gas phase through isomer-selective, tunable, soft photoionization reflectron time-of-flight mass spectrometry. Theoretical calculations reve...
Article
We investigated the formation of small organosilicon molecules─potential precursors to silicon-carbide dust grains ejected by dying carbon-rich asymptotic giant branch stars─in the gas phase via the reaction of atomic carbon (C) in its 3P electronic ground state with silane (SiH4; X1A1) using the crossed molecular beams technique. The reactants col...
Article
The subvalent germanium monoxide (GeO, X1Σ+) molecule has been prepared via the elementary reaction of atomic germanium (Ge, 3Pj) and molecular oxygen (O2, X3Σg-) with each reactant in its electronic ground state by means of single-collision conditions. The merging of electronic structure calculations with crossed beam experiments suggests that the...
Article
The silyl cyanide (SiH3CN) molecule, the simplest representative of a fully saturated silacyanide, was prepared in the gas phase under single-collision conditions via a radical substitution mechanism. The chemical dynamics were direct and revealed a pronounced backward scattering as a consequence of a transition state with a pentacoordinated silico...
Article
Full-text available
Polycyclic aromatic hydrocarbons (PAHs) are prevalent in deep space and on Earth as products in combustion processes bearing direct relevance to energy efficiency and environmental remediation. Reactions between hydrocarbon radicals in particular have been invoked as critical molecular mass growth processes toward cyclization leading to these PAHs....
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Full-text available
The Strecker Synthesis of (a)chiral α-amino acids from simple organic compounds, such as ammonia (NH 3 ), aldehydes (RCHO), and hydrogen cyanide (HCN) has been recognized as a viable route to amino acids on primordial earth. However, preparation and isolation of the simplest hemiaminal intermediate – the aminomethanol (NH 2 CH 2 OH)– formed in the...
Article
Full-text available
Significance Methanediol [CH 2 (OH) 2 ] represents a pivotal atmospheric volatile organic compound and plays a fundamental role in aerosol growth. Although sought for decades, methanediol has never been identified due to the inherent dehydration tendency of two adjacent hydroxyl groups (OH) at the same carbon atom. Here, we prepare and identify met...
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Resonantly stabilized free radicals (RSFRs) have been contemplated as fundamental molecular building blocks and reactive intermediates in molecular mass growth processes leading to polycyclic aromatic hydrocarbons (PAHs) and carbonaceous nanoparticles on Earth and in deep space. By combining molecular beams and computational fluid dynamics simulati...
Article
We report the results on the combustion of single, levitated droplets of exo-tetrahydrodicyclopentadiene (JP-10) doped with titanium-aluminum-boron (Ti-Al-B) reactive metal nanopowders (RMNPs) in an oxygen (60%)-argon (40%) atmosphere by exploiting an ultrasonic levitator with droplets ignited by a carbon dioxide laser. Ultraviolet-visible (UV-vis)...
Article
The hitherto elusive monobridged Ge( µ -H)GeH (X 1 A') molecule was prepared in gas phase through bimolecular reaction of atomic germanium (Ge) with germane (GeH 4 ). Merged with electronic structure calculations, this reaction was revealed to commence on the triplet surface with the formation of a van der Waals complex, followed by insertion of ge...
Article
The gas-phase reaction of the methylidyne (CH; X ² Π) radical with dimethylacetylene (CH 3 CCCH 3 ; X ¹ A 1g ) was studied at a collision energy of 20.6 kJ mol ⁻¹ under single collision conditions with experimental results...
Article
We report the detection of two isomers of ethynyl cyclopentadiene ( c -C 5 H 5 CCH), namely 1- and 2-ethynyl-1,3-cyclopentadiene, in the direction of TMC-1. We derive column densities of (1.4 ± 0.2) × 10 ¹² cm ⁻² and (2.0 ± 0.4) × 10 ¹² cm ⁻² , respectively, for these two cyclopentadiene derivatives, which imply that they are about ten times less a...
Preprint
Full-text available
We report the detection of two isomers of ethynyl cyclopentadiene (c-C5H5CCH), namely 1- and 2-ethynyl-1,3-cyclopentadiene, in the direction of TMC-1. We derive column densities of (1.4 +/- 0.2)e12 cm-2, and (2.0 +/- 0.4)e12 cm-2, respectively, for these two cyclopentadiene derivatives, which imply that they are about ten times less abundant than c...
Article
Kinetics of ozone destruction due to the recombination of oxygen atoms produced by pulsed 266 nm laser photolysis of O3/M (M = CO2 and/or N2) mixtures was studied using the absorption and emission spectroscopy to follow time evolutions of O3 and electronically excited molecules O2* formed in the recombination process 2O(³P) + M ® O2*+ M. An unexpec...
Article
The observation of complex organic molecules (COMs) in the gas phase of cold molecular clouds has coined a freeze-out paradox in astrophysics: COMs should be accreted on low-temperature interstellar grains, but not observable in cold molecular clouds. Still, validated mechanisms transporting molecules from the grains back into the gas phase are sti...
Article
Full-text available
Polyhedral nitrogen containing molecules such as prismatic P3N3 - a hitherto elusive isovalent species of prismane (C6H6) - have attracted particular attention from the theoretical, physical, and synthetic chemistry communities. Here we report on the preparation of prismatic P3N3 [1,2,3-triaza-4,5,6-triphosphatetracyclo[2.2.0.02,6.03,5]hexane] by e...
Article
Full-text available
Despite remarkable progress toward the understanding of the formation pathways leading to polycyclic aromatic hydrocarbons (PAHs) in combustion systems and in deep space, the complex reaction pathways leading to nitrogen-substituted PAHs (NPAHs) at low temperatures of molecular clouds and hydrocarbon-rich, nitrogen-containing atmospheres of planets...
Article
The reaction of the D1-silylidyne radical (SiD; X2Π) with phosphine (PH3; X1A1) was conducted in a crossed molecular beams machine under single collision conditions. Merging of the experimental results with ab initio electronic structure and statistical Rice-Ramsperger-Kassel-Marcus (RRKM) calculations indicates that the reaction is initiated by th...
Article
We report the detection, for the first time in space, of a new non-functionalised hydrocarbon cycle in the direction of TMC-1: o -C 6 H 4 (ortho-benzyne). We derive a column density for this hydrocarbon cycle of (5.0 ± 1.0) × 10 ¹¹ cm ⁻² . The abundance of this species is around 30 times lower than that of cyclopentadiene and indene. We compare the...
Preprint
Full-text available
We report the detection, for the first time in space, of a new non-functionalised hydrocarbon cycle in the direction of TMC-1: o-C6H4 (ortho-benzyne). We derive a column density for this hydrocarbon cycle of (5 +/- 1)e11 cm-2. The abundance of this species is around 30 times lower than that of cyclopentadiene and indene. We compare the abundance of...
Article
he formation of complex organic molecules by energetic electrons mimicking secondary electrons generated within trajectories of galactic cosmic rays was investigated in interstellar ice analog samples of carbon monoxide and water at 5 K. Simulating the transition from cold molecular clouds to star-forming regions, newly formed products sublimed dur...
Article
The reactions of the D1-silylidyne radical (SiD; X2Π) with deuterium sulfide (D2S; X1A1) and hydrogen sulfide (H2S; X1A1) were conducted utilizing a crossed molecular beams machine under single collision conditions. The experimental work was carried out in conjunction with electronic structure calculations. The elementary reaction commences with a...
Article
Full-text available
Sulfur- and silicon-containing molecules are omnipresent in interstellar and circumstellar environments, but their elementary formation mechanisms have been obscure. These routes are of vital significance in starting a chain of chemical reactions ultimately forming (organo) sulfur molecules—among them precursors to sulfur-bearing amino acids and gr...
Article
Full-text available
The surface mineralogy of dwarf planet Ceres is rich in ammonium (NH 4 ⁺ ) bearing phyllosilicates. However, the origin and formation mechanisms of ammoniated phyllosilicates on Ceres’s surface are still elusive. Here we report on laboratory simulation experiments under astrophysical conditions mimicking Ceres’ physical and chemical environments wi...
Article
The chemical dynamics of the elementary reaction of ground state atomic silicon (Si; 3 P) with germane (GeH 4 ; X 1 A 1 ) were unraveled in the gas phase under single collision condition at a collision energy of 11.8 ± 0.3 kJ mol ‐1 exploiting the crossed molecular beams technique contemplated with electronic structure calcu­la­tions. The reaction...
Article
Full-text available
Polycyclic aromatic hydrocarbons (PAHs) have been invoked in fundamental molecular mass growth processes in our galaxy. We provide compelling evidence of the formation of the very first ringed aromatic and building block of PAHs-benzene-via the self-recombination of two resonantly stabilized propargyl (C3H3) radicals in dilute environments using is...
Article
Owing to the unique conditions in cold molecular clouds, enols—the thermody­namically less stable tautomers of aldehydes and ketones—do not undergo tautomerization to their more stable tautomers in the gas phase because they cannot overcome tautomerization barriers at the low temperatures. Laboratory studies of interstellar analog ices have demonst...
Article
We present the first formation of the previously elusive phosphine imide (HN[double bond, length as m-dash]PH3) along with its phosphinous amide (H2N–PH2) isomer via exposure of phosphine (PH3) and ammonia (NH3) ices to ionizing radiation
Article
While gas-phase astrochemical reaction networks nicely replicate the abundance of hydrogen-deficient organics like linear cyanopolyynes, pathways to complex organic molecules (COMs)—organic molecules with six or more atoms—have not been completely understood, with gas-phase models often significantly underestimating fractional abundances of the ast...
Article
This Perspective presents recent advances in our knowledge of the fundamental elementary mechanisms involved in the low- and high-temperature molecular mass growth processes to polycyclic aromatic hydrocarbons in combustion systems and in extraterrestrial environments (hydrocarbon-rich atmospheres of planets and their moons, cold molecular clouds,...
Article
Ices of acetylene (C 2 H 2 ) and ammonia (NH 3 ) were irradiated with 5 keV electrons to simulate interstellar ices processed by galactic cosmic rays in order to investigate the formation of C 2 H 3 N isomers. Supported by quantum chemical calculations, experiments detected product molecules as they sublime from the ices using photoionization refle...
Article
Nitrogen dioxide (NO2) can significantly improve the combustion of hydrocarbon fuels, but the effect of NO2 on the ignition of fuels with energy densities enhanced by aluminum (Al) nanoparticles has not been studied. We therefore investigated the effects of NO2 on the ignition of JP-10 droplets containing Al nanoparticles initially acoustically lev...
Article
Small silicon hydrides have attracted extensive interest because of their role in the chemical evolution of circumstellar envelopes of evolved carbon stars and applications in surface growth processes and as transients in semiconductor manufacturing. Combined with electronic structure calculations, we demonstrate that monobridged silylidynesilylene...
Article
The phosphinidenesilylene (HPSi; X1A') molecule was prepared via a directed gas-phase synthesis in the bimolecular reaction of ground-state atomic silicon (Si; 3P) with phosphine (PH3; X1A1) under single-collision conditions. The chemical dynamics are initiated on the triplet surface via addition of a silicon atom to the non-bonding electron pair o...
Article
Fullerenes (C60, C70) detected in planetary nebulae and carbonaceous chondrites have been implicated to play a key role in the astrochemical evolution of the interstellar medium. However, the formation mechanism of even their simplest molecular building block — the corannulene molecule (C20H10) — has remained elusive. Here we demonstrate via a comb...