A Theoretical Study of the CH₂N System:  Reactions in both Lowest Lying Doublet and Quartet States

Abstract

Ab initio molecular orbital calculations at the second-order perturbation theory (UMP2) and coupled cluster singles and doubles with corrected triples (CCSD(T)) levels with 6-311++G(d,p) and 6-311++G(3df,3dp) basis sets have been carried out to construct the potential energy surfaces related to the various reactions of the [CH2N] system, including H2+CN, H+HCN, and H+HNC in both lowest lying doublet and quartet electronic states. Barrier heights, vibrational wavenumbers, and moments of inertia were then utilized in the calculations of rate constants using a quantum Rice−Ramsperger−Kassel (QRRK) theory. The calculated total rate constant k ∞ for the H+HCN reaction at 300 K is 2.2 × 107 cm3 mol-1 s-1 and is suggestive of a slow reaction and it corresponds predominantly to the stabilization of the adducts. On the other hand, the H+HNC reaction is calculated to be a pressure-independent fast reaction with a rate coefficient of 1.9 × 1011 cm3 mol-1 s-1 leading primarily to H+HCN dissociation products. The standard heat of formation of the H2CN radical is estimated to be Δ = 56 ± 3 kcal/mol (57 ± 3 kcal/mol at 0 K).

Importance of the Hydrogen Isocyanide Isomer in Modeling Hydrogen Cyanide Oxidation in Combustion

“…Also, reaction R12b has been studied theoretically; 85,87 we have included this step in the exothermic direction, HNC + H ⇌ HCN + H (R12), with a rate constant calculated by Sumathi and Nguyen. 85 The most important consumption reaction of HNC is presumably HNC + OH. Figure 1 shows an Arrhenius plot for the reaction.…”

The interstellar gas-phase chemistry of HCN and HNC

“…The main HNC production is then only the DR of HCNH + after proton exchange from HCO + and H 3 + to HCN. Moreover, if the O + HCN reaction shows a relatively high barrier close to 4000 K (Sander et al 2011) and if the H + HCN reaction also shows a relatively high barrier without any exothermic exit channels (Talbi & Ellinger 1996, Sumathi & Nguyen 1998, Petrie 2002, the corresponding HNC reactions are significantly faster. The H + HNC  H + HCN reaction has been calculated to possess a barrier estimated between 800 K and 1400 K (Talbi & Ellinger 1996, Sumathi & Nguyen 1998, Petrie 2002) and the barrier for the O + HNC is calculated to be equal to 1400 K only at the M06-2X/cc-pVTZ level (this work).…”

Neutral production of hydrogen isocyanide (HNC) and hydrogen cyanide (HCN) in Titan’s upper atmosphere

“…The first estimation of the barrier was performed by Talbi & Ellinger (1996) at a relatively high level of theory (MP4/6-311++(3df,2p)//MP3/6-311++G(d,p)) with a best estimate value equal to 17.6 ± 4 kJ mol −1 . Sumathi & Nguyen (1998) found a barrier equal to 13.8 kJ mol −1 at the CCSD(T)/6-311++(3df,3pd)//CCSD(T)/6-311++G(d,p) level and more recently Petrie (2002) found a value equal to 8.0 kJ mol −1 at the CBS/RAD or B3LYP/6-311G** level and 12.9 kJ mol −1 at the QCISD/6-311G* level. With estimated values between 8.0 kJ mol −1 (960 K) and 18.0 kJ mol −1 (2160 K), the rate will be low, but not negligible, for relaxed HNC.…”

“…Moreover, as HNC is produced mainly with high internal energy there is a possibility of rate enhancement. For relaxed HNC we recommend the rate constant calculated by Sumathi & Nguyen (1998) The N( 2 D) + CH 4 reaction has been studied experimentally Umemoto et al 1998) and theoretically (Ouk et al 2011;) and a review has been performed by Herron (1999). Theoretical calculations suggest two pathways for this reaction, direct H atom abstraction and N( 2 D) insertion in one C-H bond, both mechanism presenting a barrier in the entrance valley (Ouk et al 2011;.…”