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An ab initio/Rice–Ramsperger–Kassel–Marcus study of photodissociation of carbonyl cyanide
Author(s) -
Lee H. Y.,
Mebel A. M.,
Lin S. H.
Publication year - 2002
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.937
Subject(s) - chemistry , photodissociation , rrkm theory , ab initio , reaction rate constant , branching fraction , computational chemistry , ab initio quantum chemistry methods , branching (polymer chemistry) , molecule , atomic physics , photochemistry , kinetics , physics , quantum mechanics , organic chemistry
The geometries and vibrational frequencies of the parent molecule, intermediates, transition state, and products involved in the photochemical decay of carbonyl cyanide NC–C(O)–CN have been studied by ab initio calculations at the MP2/6‐311G* level. The energies of various species have been refined using the modified Gaussian‐2 [G2M(MP2)] method. The molecular parameters and energetics derived from the ab initio calculations were used to compute microcanonical rate constants of all possible reaction steps of photodissociation of the carbonyl cyanide employing the conventional and variational RRKM theory and to obtain the product branching ratios. The results show that the radical decay, CO(CN) 2 + h ν→OCCN/OCNC+CN, is dominant (86.14% and 13.85% for OCCN and OCNC, respectively), while the molecular decay, CO(CN) 2 →CO+NCCN, gives only a trace amount of the products. Whereas the computed radical product yields qualitatively agree with those measured in experiment (Scheld, H. A., et al. J Chem Phys 1999, 111, 923), the calculated branching ratio for the molecular decay channel underestimates the experimental value of ∼6%. This deviation may be attributed to the deficiencies in the variational RRKM treatment of the radical decay rate constants and/or to some nonstatistical behavior of the system which enhances the molecular decay. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002