Photodissociation dynamics of the singlet and triplet states of the NCN radical

Abstract

Ultraviolet photodissociation dynamics of the SH radical J. Chem. Phys. 123, 054330 (2005); 10. 1063/1.1961565 193-nm photodissociation of acryloyl chloride to probe the unimolecular dissociation of CH 2 CHCO radicals and CH 2 CCO -ã 1 ⌬ g transitions were examined. The major dissociation products for the B 3 ⌺ u Ϫ and c 1 ⌸ u statesϪ state at photon energies greater than 4.9 eV, where it comprises Ϸ25Ϯ10% of the total signal. At all photon energies, the photofragment translational energy distributions show a resolved progression corresponding to the vibrational excitation of the N 2 photofragment. The rotational distributions of the molecular fragments suggest that the dissociation pathway for the N 2 loss channel involves a bent transition state while the NϩCN photofragments are produced via a linear dissociation mechanism. The P(E T ) distributions provide bond dissociation energies of 2.54Ϯ0.030 and 4.56Ϯ0.040 eV for the N 2 and CN loss channels, respectively, yielding ⌬H f ,0 K ͑NCN͒ϭ4.83Ϯ0.030 eV.

The CH+N2 reaction over the ground electronic doublet potential energy surface: a detailed transition state search

“…The apparent barrier for the HNCN dissociation would be much lower at high temperatures because of the entropic contribution, which reduces the values of DG z as the temperature increases. The theoretically predicted heat of formation for the NCN radical at 0 K based on reaction (2), 111.0 kcal/ mol, is in excellent agreement with the recently reported experimental value by Bise et al [30], 111X3 AE 0X7 kcal/mol. The predicted dissociation energy, D 0 H±NCN 84X0 kcal/mol also compares well with the value, 81X7 AE 1X0 kcal/mol reported by Cliord et al [31].…”

“…The predicted dissociation energy, D 0 H±NCN 84X0 kcal/mol also compares well with the value, 81X7 AE 1X0 kcal/mol reported by Cliord et al [31]. Their experimental heat of formation for the NCN radical is D f H 0 107X4 AE 3X2 kcal/mol, somewhat lower than that of Bise et al [30] as given.…”

Ab initio study of the oxidation of NCN by O2

“…Based on the known experimental heats of formation (at 0 K) of NCN (111.3 ± 0.7 kcal/mol) [15], NO (21.46 ± 0.04 kcal/mol) [16], and the predicted exothermicity of the reaction NCN + O 2 → NCO + NO, 60.0 kcal/mol, the heat of formation of NCO is calculated to be 29.8 ± 0.7 kcal/mol. It is in close agreement with the experimental value, 30.4 ± 1.0 kcal/mol [17].…”

State-resolved translation energy distributions for NCO photodissociation

“…The details of this procedure have been described previously. 38 The resulting vibrational distributions are presented in Table I. Although vibrational levels beyond ϭ2 for the 1 0 2 transition and ϭ3 for the 3 0 1 transition are populated, the features were not of sufficient resolution to permit acceptable modeling by this method; Table I shows populations only for those vibrational levels that can be resolved.…”

“…Although the mass resolution of these experiments hinders the separation of the two mass channels, in previous studies of NCN and CNN we observed the presence of a N 2 ϩC mass channel that was energetically overlapped with a CNϩN mass channel. 38,39 A broadening and shifting of the peaks in the mass spectrum from those of a single channel marked the presence of both channels. A similar trend was not observed in the mass spectrum of the products of NCO photodissociation, indicating that the contribution from the OϩCN mass channel is not substantially greater than the contribution from the NϩCO mass channel in the region of E T р0.71 eV.…”