Kinetics Of The H + CH₂ → CH + H₂ Reaction At Low Temperature

Abstract

A quasiclassical trajectory study of the kinetics of the title astrochemical reaction in a range of temperatures varying from 5 to 1000 K (corresponding to both the outer and the inner regions of the protostar and the circumstellar envelopes) was carried out and a clear dependence of the rate coefficient on the temperature is given, in contrast with the constant value adopted in kinetics astrochemical databases. Levering the massive nature of the performed calculations and of the detailed dynamical investigation of the reactive process, a rationalization of the temperature dependence of the released translational energy and of the rovibrational population of the CH and H 2 diatomic products is also provided. Furthermore, the effect of the initial rovibrational energy of CH 2 on the state-specific rate coefficients and cross sections is analyzed in order to single out the role played by the different regions of the potential energy surface on the dynamical outcomes and on the modeling the temperature dependence of the reactive efficiency of the investigated process. This led to a parametrization of the computed rate in terms of the following double Arrhenius expression (in cm 3 s −1 ), k(T) = 2.50 × 10 −10 exp(− 1.67/T) + 5.98 × 10 −11 exp(− 280.5/T), alternative to the piecewise formulation into the three subintervals of temperature in which the overall 5−1000 K interval can be divided.

Studies on the Kinetics of the CH + H2 Reaction and Implications for the Reverse Reaction, 3CH2 + H

“…Figure shows the temperature dependence for k –1 based on both this work and various literature studies. This work, the theoretical calculations of Garcia et al, and the recommendations of the Baulch et al review are in excellent agreement on the lack of any significant temperature dependence, and room-temperature values vary over a relatively narrow range from (1.7 to ∼3) × 10 –10 cm 3 molecule –1 s –1 . Our result is also in excellent agreement with the room-temperature study of Bohland et al (1.83 × 10 –10 cm 3 molecule –1 s –1 ).…”

“…An important reaction of CH in combustion and in the atmospheres of the giant planets is the reaction with H 2 (reaction 1): − The CH + H 2 reaction is thought to proceed via an insertion forming chemically activated methyl radicals, CH 3 *, that can either be stabilized or eliminate a hydrogen atom to form ground-state methylene, 3 CH 2 , as the coproduct: The thermodynamics of the system is well-established, and the potential energy surface (PES) has been calculated by a number of groups (see, e.g., refs and ). A schematic of the PES is shown in Figure a.…”

Self-consistent modeling of microwave activated N2/CH4/H2 (and N2/H2) plasmas relevant to diamond chemical vapor deposition

“…The literature [77][78][79][80][81] contains a broad spread of values for the rate coefficients of the 3 CH 2 + H ↔ CH 3 * ↔ CH + H 2 conversions, which determine the CH concentrations under the prevailing conditions. The uncertainty in these rate coefficients hampers interpretation of the measured {CH} column densities.…”