Temperature dependences of methylene (~a 1A1) removal rates by argon, nitric oxide, hydrogen, and ketene in the range 295-859 K

Abstract

Absolute rate constants for the removal of CH2 (5'A,) by Ar, NO, H2, and CH2CO have been measured over the temperature range 295-859 K by the method of long-path kinetic absorption spectroscopy. For quenching to the ground X^s tate by Ar, the rate constant rises by a factor of 3 over this range from its room-temperature value. Both the absolute values and their increase up to ~500 K can be explained by a mixed-state model of quenching, in which fractional populations of singlet states perturbed by nearby triplet levels and the relaxation of the corresponding triplet levels contribute to the measured removal rate. Above 500 K, there is a significant deviation between experiment and calculation, suggesting that additional high-energy perturbed singlet levels are affecting the decay process. In contrast, removal by H2 and NO, both considered to be predominantly by reaction, shows no temperature variation over this range, while removal by ketene shows a negative temperature dependence. The implications of the results to singlet methylene quenching and reaction processes at combustion temperatures are discussed.

Mechanism and Rate Constants of the CH3+ CH2CO Reaction: A Theoretical Study

“…Reactions of ketene with hydrocarbon radicals may lead to formation of C2 hydrocarbons. These hydrocarbons are easily detected by gas analysis, whereas methylidyne CH, triplet 3 CH 2 , and singlet 1 CH 2 can be detected using laser-induced fluorescence; hence their rate constants with ketene were measured experimentally in [14,19,[34][35][36][37], and [38][39][40], respectively. Theoretically, these reactions with CH and CH 2 were addressed in [41] and [10], respectively.…”

Infrared Multiple Photon Dissociation of Chloromethyltrifluorosilane

“…Due to the spin conservation law, methylene should be formed in the singlet excited state in reaction (R.1). The energy difference between the fundamental triplet state and the first excited singlet state for methylene is about 38 kJ mol )1 (33).…”

“…are essentially high (1-2) · 10 )10 cm 3 s )1 (33,35). 1 CH 2 reactions with hydrocarbons are very fast, with rate constants approaching the gas kinetic collision efficiency, while the corresponding rate constants of 3 CH 2 are 5-6 orders of magnitude lower (33). Therefore, the end products are formed not only in primary dissociation reaction (R.2) but also in secondary reactions of 1 CH 2 formed in reaction (R.2).…”

Singlet Methylene Removal Rate Constants from the (0,1,0) Vibrational Level: Enhancement via Complex-Mediated Vibrational Relaxation

“…There are a small number of species for which the branching ratio for CIISC versus reaction has been determined and reaction rate constants extracted [11][12][13][14][15][16][17]. While the majority of the removal rate constants are for ambient temperature, there have been limited studies of the temperature dependence for approximately 20 species [15,18,21,26,30]. The large corpus of rate data has allowed a detailed picture to emerge concerning the reaction mechanisms of 1 CH 2 with a variety of organic functional groups.…”