Ab Initio Molecular Orbital Calculations for the N(²D) + Ethylene Reaction

Abstract

The lowest doublet potential energy surface for the N(2D) + C2H4 reaction has been characterized using ab initio molecular orbital theory. The CASSCF/cc-pVDZ calculations predict that the dominant mechanism is the addition of N(2D) to the CC π-bond of C2H4 to form a cyclic three-membered intermediate radical rather than the insertion into the CH bond in C2H4. Reaction pathways have also been discussed on the basis of the PMP4(full,SDTQ)/cc-pVTZ//MP2/cc-pVDZ level calculations. The reaction is shown to have several possible products via somewhat complicated reaction mechanisms. The results of RRKM calculations predict that the main product channel is cyclic-CH(N)CH2 (azirine) + H under collision-free conditions.

Gas-Phase Reactions in Extraterrestrial Environments: Laboratory Investigations by Crossed Molecular Beams

“…Our experimental results clearly indicate that also this reaction proceeds through the formation of an addition intermediate and that products of general formula C 2 H 3 N are formed through a N/H exchange channel (Balucani et al 2000a). Our findings support the PES ab initio calculations by Takayanagi et al (1998) and are consistent with the formation of ketenimine and 2H-azirine. It is very interesting to note, however, that according to the energy release -a piece of information which can be obtained only from a reaction dynamics experiment -a large fraction of the 2H-azirine and ketenimine molecules are formed with enough internal energy to spontaneously tautomerize to the most stable isomer acetonitrile, even in a collision free environment.…”

CRITICAL REVIEW OF N, N + , N + 2 , N ++ , And N ++ 2 MAIN PRODUCTION PROCESSES AND REACTIONS OF RELEVANCE TO TITAN'S ATMOSPHERE

“…So the H/D isotope effect was found to be very small. The recommended rate constant value of 6.5 × 10 −11 cm 3 s −1 for C 2 H 2 is the same as the one proposed by Herron (1999), based on the results from Takayanagi et al (1998b). It is quite significantly larger than the value postulated by Yung (1987).…”

“…Both Umemoto et al (1985) and Takayanagi et al (1999) (±25%) for C 2 H 2 k = 6.25 × 10 −11 cm 3 s −1 (±25%) for C 2 D 2 . The rate constant has been measured by two groups (Fell et al 1981;Takayanagi et al 1998b; see Table 3) measured the rate constants over the temperature range 223-293 K and reported values of k = 1.6 × 10 −10 exp (−270/T) cm 3 s −1 and 1.4 × 10 −10 exp(−240/T) for C 2 H 2 and C 2 D 2 , respectively. So the H/D isotope effect was found to be very small.…”

“…By extrapolating this variation, we thus recommend a branching ratio of (0.9 ± 0.1)/(0.1 ± 0.05) at 300 K, as well as at 150 K. Table 3). Takayanagi et al (1998b) measured the rate constants over the temperature range 223-293 K and reported values of k = 1.0 × 10 −10 exp (−440/ T) cm 3 s −1 and 7.1 × 10 −11 exp (−380/T) for C 2 H 2 and C 2 D 2 , respectively. The products of this reaction have not been measured, but the measured rate constant, which is much larger than for the reactions of N ( 2 P) with H 2 or CH 4 , suggests that the main process is chemical reaction and not N ( 2 P) quenching.…”

Elementary Reactions and Their Role in Gas-Phase Prebiotic Chemistry

“…The CMB-MS results clearly indicate that also this reaction proceeds through the formation of an addition intermediate and that products of general formula C 2 H 3 N are formed through a N/H exchange channel [116]. The experimental findings gained support from the PES calculations by Takayanagi et al [184] and are consistent with the formation of ketenimine and 2 H -azirine. It is very interesting to note, however, that according to the energy release – a piece of information which can be obtained only from a reaction dynamics experiment – a large fraction of the 2 H -azirine and ketenimine molecules are formed with enough internal energy to spontaneously tautomerize to the most stable isomer acetonitrile [116], even in a collision free environment.…”