State-resolved translation energy distributions for NCO photodissociation

Abstract

The photodissociation dynamics of NCO have been examined using fast beam photofragment translational spectroscopy. Excitation of the 1 0 2 , 3 0 1 , and 1 0 2 3 0 2 transitions of the B 2 ⌸←X 2 ⌸ band produces N( 4 S)ϩCO photofragments exclusively, while excitation of the 1 0 3 3 0 3 transition yields primarily N( 2 D)ϩCO photoproducts. The translational energy ͓ P(E T )͔ distributions yield D 0 ͑N-CO͒ϭ2.34Ϯ0.03 eV, and ⌬H f ,0 0 ͑NCO͒ϭ1.36Ϯ0.03 eV. The P(E T ) distributions exhibit vibrationally resolved structure reflecting the vibrational and rotational distributions of the CO product. The N( 2 D)ϩCO distribution can be fit by phase space theory ͑PST͒, while the higher degree of CO rotational excitation for N( 4 S)ϩCO products implies that NCO passes through a bent geometry upon dissociation. The P(E T ) distributions suggest that when the B 2 ⌸←X 2 ⌸ band is excited, NCO undergoes internal conversion to its ground electronic state prior to dissociation. Excitation of NCO at 193 nm clearly leads to the production of N( 2 D)ϩCO fragments. While conclusive evidence for the higher energy O( 3 P)ϩCN(X 2 ⌺ ϩ ) channel was not observed, the presence of this dissociation pathway could not be excluded.

Ab initio chemical kinetics for the reactions of N2 with singlet and triplet C2O radicals

“…2), the heats of reaction for the products of NCO + CN, 3 CNN + CO and 3 NCN + CO are 45.9, 18.1 and À10.7 kcal/mol. They are in excellent agreement with the experimental values, 45.8, 17.7 and À10.7 kcal/mol based on the known experimental heats of formation (at 0 K) of CCO (91.1 ± 0.5 kcal/mol) [26]; NCO (31.4 ± 0.7 kcal/mol) [29]; CNN (136 ± 5 kcal/mol) [30]; CN (105.5 ± 2 kcal/mol kcal/mol) [31]; NCN (107.6 ± 3.2 kcal/mol) [32] and CO (À27.2 ± 0.04) [31].…”

On the statisticodynamical approach of final state distributions in simple bond fissions

“…By internal conversion or intersystem crossing, the system eventually turns back to the ground electronic state and the dissociation ABC -AB þ C follows. 8,9 In such a process, the average magnitude of the total angular momentum is usually so low that it is considered as zero in most theoretical developments. 1 R E S E A R C H P A P E R PCCP www.rsc.org/pccp A short time after the return to the ground electronic state (with respect to the average time for dissociation), the phase space state distribution of ABC is supposed to be microcanonical, due to strong couplings between its various degrees of freedom (assumption 1).…”

“…were measured experimentally by Neumark et al 8,9 PST was applied to their description 7 and as can be seen in Figs. 1 and 2, satisfying agreement between theory and experiment was found as far as the gross features of the distributions are concerned.…”

Ab initio chemical kinetics for the reactions of HNCN with O(3P) and O2

“…The predicted heats of reaction for the formation of NO + CNH, OH + 3 NCN, and CN+HNO from the O( 3 P) + HNCN are in reasonable agreement with the available experimental values at 0 K, À66.1 ± 1.6 kcal/mol, À15.4 ± 4.6 kcal/mol, and À2.4 ± 1.4 kcal/mol, respectively, based on the heats of formation D f H 0 at 0 K as the following: D f H 0 (O) = 59.56 ± 0.02 kcal/mol [16]; D f H 0 (HNCN) = 72.3 ± 0.7 kcal/mol [5]; D f H 0 (NO) = 21.456 kcal/mol [17]; D f H 0 (CNH) = 44.3 ± 0.9 kcal/mol [5]; D f H 0 (OH) = 8.87 ± 0.07 kcal/mol [16]; D f H 0 ( 3 NCN) = 107.6 ± 3.2 kcal/mol derived from D f H 298 ( 3 NCN) = 107.7 ± 3.2 kcal/mol [4]; D f H 0 (CN) = 104.1 ± 0.5 kcal/mol [5]; D f H 0 (HNO) = 24.5 kcal/mol [17]. Comparing with the available experimental heat of reaction producing 3 NH + NCO, À15.2 ± 1.6 kcal/mol based on the experimental heats of formation, D f H 0 ( 3 NH) = 85.29 ± 0.14 kcal/mol [18] and D f H 0 (NCO) = 31.36 ± 0.69 kcal/mol [19], our predicted value (À20.9 kcal/mol) is about 5.7 ± 1.6 kcal/mol lower than the experimental data. However, the predicted result is close to the value, À21.8 ± 0.7 kcal/mol, based on the computed heats of formation, D f H 0 ( 3 NH) = 79.6 kcal/mol [20] and D f H 0 (NCO) = 30.5 kcal/mol [21].…”