The photodissociation of formaldehyde: A coupled cluster study including connected triple excitations of the transition state barrier height for H2CO→H2+CO

Ab initio molecular quantum mechanics has been applied to the unimolecular dissociation of H2CO. Basis sets as large as triple zeta plus double polarization (TZ+2P) were used in conjunction with complete optimization of all stationary point geometries. The classical barrier height is predicted with the TZ+2P basis set to be 101.9 (SCF), 95.0 (CISD), 90.4 (CCSD), and 86.8 kcal/mol (CCSDT‐1). With correction for zero‐point vibrational energies, the activation energy is predicted to be 81.4 kcal/mol, in good agreement with experimental estimates.

[1]  G. Diercksen,et al.  Can the coupled cluster method improve many-body perturbation theory reaction energies significantly? the H2CO → H2 + CO reaction , 1987 .

[2]  D. R. Stull.  JANAF thermochemical tables , 1966 .

[3]  Toru Nakagawa,et al.  Band contour analysis of the nu1 and nu5 fundamentals of formaldehyde , 1971 .

[4]  Michael J. Frisch,et al.  The lowest singlet potential surface of formaldehyde , 1981 .

[5]  Michael J. Frisch,et al.  Self‐consistent molecular orbital methods 25. Supplementary functions for Gaussian basis sets , 1984 .

[6]  G. Scuseria,et al.  Analytic evaluation of energy gradients for the single, double and linearized triple excitation coupled-cluster CCSDT-1 wavefunction: Theory and applications , 1988 .

[7]  R. Bartlett,et al.  A study of Be2 with many‐body perturbation theory and a coupled‐cluster method including triple excitations , 1984 .

[8]  Lawrence B. Harding,et al.  Vibrational energy levels of formaldehyde , 1985 .

[9]  C. Moore,et al.  Photofragmentation dynamics of formaldehyde: CO(v,J) distributions as a function of initial rovibronic state and isotopic substitution , 1985 .

[10]  G. Herzberg,et al.  Constants of diatomic molecules , 1979 .

[11]  Michael J. S. Dewar,et al.  Development and status of MINDO/3 and MNDO , 1983 .

[12]  Paul J. Crutzen,et al.  Evaluated Kinetic and Photochemical Data for Atmospheric Chemistry: Supplement I CODATA Task Group on Chemical Kinetics , 1982 .

[13]  Henry F. Schaefer,et al.  Features of the H2CO potential energy hypersurface pertinent to formaldehyde photodissociation , 1981 .

[14]  T. H. Dunning.  Gaussian Basis Functions for Use in Molecular Calculations. III. Contraction of (10s6p) Atomic Basis Sets for the First‐Row Atoms , 1970 .

[15]  Julia E. Rice,et al.  Analytic evaluation of energy gradients for the single and double excitation coupled cluster (CCSD) wave function: Theory and application , 1987 .

[16]  W. Miller.  Tunneling Corrections to Unimolecular Rate Constants, with Application to Formaldehyde , 1979 .

[17]  B. Roos,et al.  A complete active space SCF method (CASSCF) using a density matrix formulated super-CI approach , 1980 .

[18]  Ernest R. Davidson,et al.  Configuration interaction calculations on the nitrogen molecule , 1974 .

[19]  H. Petek,et al.  Understanding Molecular Dynamics Quantum-State by Quantum-State , 1985, Science.

[20]  John W. Tukey,et al.  CRITICAL EVALUATION OF CHEMICAL AND PHYSICAL STRUCTURAL INFORMATION. , 1800 .

[21]  C. Moore,et al.  Photofragmentation dynamics of formaldehyde: H2(v, J) distributions , 1985 .

[22]  J. Pople,et al.  Self‐consistent molecular orbital methods. XX. A basis set for correlated wave functions , 1980 .

[23]  C. Moore,et al.  T1 barrier height, S1–T1 intersystem crossing rate, and S0 radical dissociation threshold for H2CO, D2CO, and HDCO , 1987 .

[24]  Bernard R. Brooks,et al.  Analytic gradients from correlated wave functions via the two‐particle density matrix and the unitary group approach , 1980 .

[25]  H. Schaefer,et al.  Abinitio calculation of reaction energies. III. Basis set dependence of relative energies on the FH2 and H2CO potential energy surfaces , 1984 .

[26]  Robert L. Kuczkowski,et al.  Molecular structures of gas‐phase polyatomic molecules determined by spectroscopic methods , 1979 .

[27]  H. Schaefer,et al.  A New dimension to quantum chemistry: Theoretical methods for the analytic evaluation of first, second, and third derivatives of the molecular electronic energy with respect to nuclear coordinates , 1986 .

[28]  William F. Polik,et al.  Dissociation rates for individual eigenstates of S0 formaldehyde: Fluctuations and barrier height , 1986 .

[29]  W. A. Lester,et al.  Formaldehyde: Abinitio MCSCF+CI transition state for H2CO → CO+H2 on the S0 surface , 1983 .

[30]  Paul H. Krupenie.  The band spectrum of carbon monoxide , 1966 .