Unimolecular decomposition of chemically activated deutero-substituted ethanol molecules studied by infrared chemiluminescence from H2O, HOD, and D2O

Abstract

The isotope effect in solvation dynamics and nonadiabatic relaxation: A quantum simulation study of the photoexcited solvated electron in D2OThe farinfrared vibration-rotation-tunneling spectrum of the water tetramerd8 with an excitation energy of about 100 kcal mol Ϫ1 were observed by infrared chemiluminescence in the 2400-3900 cm Ϫ1 range. The activated ethanol molecules were produced via the successive reactions HϩCH 2 ICH 2 OH→HIϩCH 2 CH 2 OH and HϩCH 2 CH 2 OH→CH 3 CH 2 OH* in a fast flow reactor that was observed with a Fourier transform spectrometer. The vibrational distributions of the H 2 O, HOD, and D 2 O molecules were determined by computer simulation of the experimental spectra; the distributions decline with increasing vibrational energy giving ͗ f v ͘ϭ0.15 and ͗ f v ͘ϭ0.14 for H 2 O and HOD from the decomposition of C 2 H 5 OH* and C 2 H 5 OD*, respectively.The vibrational energy in the bending mode of H 2 O is comparable to the energy in the stretching modes. Comparison with the statistical vibrational distributions shows a substantial overpopulation of the bending levels and a preferential excitation of one O-H or O-D stretching quantum in HOD from C 2 H 5 OD or CH 2 DCH 2 OH, respectively, i.e., in the newly formed bond. Kinetic isotope effects of ͓H 2 O͔/͓HOD͔ϭ3.6Ϯ0.8 and ͓HOD͔/͓D 2 O͔ϭ3.1Ϯ0.8 were found for the two elimination pathways of CH 2 DCH 2 OH* and CH 2 DCH 2 OD*, respectively, which agree with calculated RRKM values of k H 2 O /k HOD ϭ 3.2 and k HOD /k D 2 O ϭ 2.7.

A detailed chemical kinetic model for high temperature ethanol oxidation

“…The Tsang [62] and the Zhitneva and Pshezhetskii [60] rate constants were derived by examining the rate constants measured for analogous reactions that eliminate water. The Tsang and Zhitneva activation energy choices were higher than those found in the recent Butkovskaya and Setser [57,58] analysis and the Herzler, Manion, and Tsang [56] recommendation. Butkovskaya and Setser performed ab initio and RRKM calculations on ethanol and the four-centered dehydration transition state step using MP2(FC)/6 -31G(d) and MP2(Full)/6 -311G(d,p) levels of theory.…”

“…Benson's rules for transition state frequencies [34] were applied, and a critical energy was selected to match the literature reviewed critical and activation energies. These critical energies are 64.0 -67.0 kcal/ mol [57,58] and 91.9 kcal/mol [59,60] [59]. d [52].…”

Product Branching Fractions and Kinetic Isotope Effects for the Reactions of OH and OD Radicals with CH3SH and CH3SD

“…The uncertainty is taken as the half of the population in the dark, ground vibrational state from the calculated statistical distribution. The population is close to the statistical distribution, P 3 (0:1:2) = 75:21:4, and the similarity to the HOD distribution from the unimolecular decomposition of CH 2 DCH 2 OH should be noted 2 Comparison of experimental and calculated spectra from the OH + CH 3 SD reaction.…”

“…Our calculation 28b reproduced the structure and frequencies for DMS·OH reported by McKee, and the frequencies selected for the CH 3 S(OH)H and CH 3 S(OD)H adducts (see Table ) should be reasonable estimates. The frequencies of the OH or OD vibrations in the TS (stretching and in-plane and out-plane bendings) were assumed to be equal to the corresponding TS frequencies for the four-centered unimolecular decomposition reactions CH 2 DCH 2 OH → H 2 O and CH 2 DCH 2 OD → HOD that were obtained by ab initio calculation at the MP2(FULL)/6-311G(d) level . The frequencies of the S−O−H‘ three-membered ring are less sensitive to the OD for OH substitution, and we choose two, which could most reliably represent the S−O and O−H‘ stretchings.…”

Infrared Chemiluminescence Studies of the H + (CH3)3COCl and H + RC(O)SCl (R = Cl, F, OCH3) Reactions: Observation of OCS Infrared Chemiluminescence

“…The infrared chemiluminescence (IRCL) technique is an established method to measure vibrational, and even rotational, product state distributions and rate constants from reactions giving HX products (X = O, F, Cl, Br). , This laboratory has employed infrared emission from a flow reactor to characterize the reaction kinetics and the vibrational distributions of many primary and secondary reactions involving both uni- and bimolecular elementary steps giving HX products. More recently, the flow reactor technique was extended to observe infrared spectra from triatomic product molecules, including H 2 O, HOD, D 2 O, − CO 2 ,3a HNO, HCN, and HNC . The vibrational distributions for the molecules just mentioned were assigned by computer simulation of the spectra obtained at experimental conditions that were chosen to avoid vibrational relaxation.…”