Reactions of Atomic Carbon with Butene Isomers: Implications for Molecular Growth in Carbon-Rich Environments

Abstract

Product detection studies of C(P) atom reactions with butene (CH) isomers (but-1-ene, cis-but-2-ene, trans-but-2-ene) are carried out in a flow tube reactor at 353 K and 4 Torr under multiple collision conditions. Ground state carbon atoms are generated by 248 nm laser photolysis of tetrabromomethane, CBr, in a buffer of helium. Thermalized reaction products are detected using synchrotron tunable VUV photoionization and time-of-flight mass spectrometry. The temporal profiles of the detected ions are used to discriminate products from side or secondary reactions. For the C(P) + trans-but-2-ene and C(P) + cis-but-2-ene reactions, various isomers of CH and CH are identified as reaction products formed via CH and H elimination. Assuming equal ionization cross sections for all CH and CH isomers, CH:CH branching ratios of 0.63:1 and 0.60:1 are derived for the C(P) + trans-but-2-ene and the C(P) + cis-but-2-ene reactions, respectively. For the C(P) + but-1-ene reaction, two reaction channels are observed: the H-elimination channel, leading to the formation of the ethylpropargyl isomer, and the CH + CH channel. Assuming equal ionization cross sections for ethylpropargyl and CH radicals, a branching ratio of 1:0.95 for the CH + CH and H + ethylpropargyl channels is derived. The experimental results are compared to previous H atom branching ratios and used to propose the most likely mechanisms for the reaction of ground state carbon atoms with butene isomers.

CRF-PEPICO: Double velocity map imaging photoelectron photoion coincidence spectroscopy for reaction kinetics studies

“…Photoionization mass spectrometry (PIMS) 1-4 is a universal, sensitive, selective, and multiplexed analytical technique to interrogate chemical reactions and has been very productive at tunable vacuum ultraviolet synchrotron light sources 5 in combustion studies, 6 among numerous other fields. 7 At the Chemical Dynamics Beamline of the Advanced Light Source, the time-resolved multiplexed photoionization mass spectrometer (MPIMS) 5 has detected and enabled the study of longsought reactive intermediates important in combustion 8,9 and atmospheric 10,11 chemistry, and has provided isomer-resolved product studies of chemistry relevant to astrochemical environments [12][13][14] including Titan, Saturn's largest moon. 15 More a) Authors to whom correspondence should be addressed: bsztaray@ pacific.edu and dlosbor@sandia.gov specifically, it enables the study of bimolecular chemical reactions by observing all reactants and products simultaneously, with enough dynamic range (10 5 ) to detect minor concentrations of key reactive intermediates in the presence of other species at much higher concentrations.…”

Product Detection of the CH Radical Reactions with Ammonia and Methyl-Substituted Amines

“…28,52 The three body reaction of the CH ( 2 , v=0) radical with molecular nitrogen is slow 53 at the pressure of the flow and is unlikely to affect the observed product distributions. Reactions of CBr with small unsaturated hydrocarbons are several orders of magnitude slower at the present temperature 46,47,50,[54][55][56] than those for reactions of the CH radical. 54,55,57,58 Similarly slow kinetics between CBr and amines would allow discriminating between CBr and CH reaction products.…”

“…Details about the calculations have been discussed elsewhere. 41,42,46,47 Heats of reaction, and adiabatic and vertical ionization energies, are calculated using the CBS-QB3 composite method. 48,49 Simulated Franck−Condon factors of isomer species are calculated at room temperature with the G09 package within the Franck−Condon approximation.…”

Design and performance of an E-band chirped pulse spectrometer for kinetics applications: OCS – He pressure broadening

“…To investigate chemical kinetics with the CRESU technique, laser spectroscopy has most often been used to detect species of interest with high sensitivity, but this spectroscopic technique can only follow one reactant or product at a time [3]. Multiplexed detection of products by tunable VUV synchrotron photoionization mass spectrometry has been applied with great success to the determination of product branching ratios at room temperature and above [4][5][6], and using a pulsed version of the CRESU technique to a few reactions down to 70 K [7,8].…”