Accurate calculations on excited states: new theories applied to the –OX, –XO, and –XO2 (X=Cl and Br) chromophores and implications for stratospheric bromine chemistry

Abstract Electronic excitation energies are determined using single-reference based theories derived from response equations involving perturbation theory and coupled-cluster theory. These methods are applied to the singlet manifold of excited electronic states of the HClO, HBrO, HOClO, HOBrO, HClO2, and HBrO2 molecules. Vertical excitation energies (VEEs) for the lowest symmetry unique triplet states are also computed using coupled-cluster theory. Both the singlet and triplet coupled-cluster VEEs are found to be in excellent agreement with experiment for HOBr and HOCl. The reliability of the various perturbation theory approaches is assessed by comparison to the linear response coupled-cluster method, and the CIS(D3) approach is found to perform the best, on average. In order to obtain reliable VEEs for these molecules, CIS(D3) is the recommended approach, unless excited state non-dynamical electron correlation is significant, in which case the recently proposed CIS(D0) technique may perform better, on average. For both the HClO2 and HBrO2 molecules, it is found that the lowest singlet excited electronic state occurs at too high an energy for it to be accessible from solar radiation in the lower stratosphere. The stratospheric chemistry implications of this, especially for bromine chemistry are discussed. It is suggested that YBrO2 molecules may in fact be the only stable stratospheric bromine reservoir species under light conditions.

[1]  Martin Head-Gordon,et al.  Single-reference theories of molecular excited states with single and double substitutions , 1993 .

[2]  M. Molina,et al.  Ultraviolet spectrum of hypochlorous acid , 1978 .

[3]  Poul Jørgensen,et al.  Perturbative triple excitation corrections to coupled cluster singles and doubles excitation energies , 1996 .

[4]  S. Iwata,et al.  Theoretical study of the photodissociation cross sections and the photodissociation dynamics of HOCl , 1992 .

[5]  Timothy J. Lee,et al.  STRUCTURES, RELATIVE STABILITIES, AND SPECTRA OF ISOMERS OF HCLO2 , 1994 .

[6]  M. Head‐Gordon,et al.  A diagnostic for the applicability of the CIS and CIS(D) excitation energy methods , 1997 .

[7]  K. Christe,et al.  Reactions of ozone with covalent hypohalites , 1974 .

[8]  Roderic L. Jones,et al.  UV-visible absorption cross sections of gaseous Br 2 O and HOBr , 1996 .

[9]  A. N. Syverud,et al.  Thermodynamic properties of diatomic gases at high temperatures: An improved calculational approach for the JANAF thermochemical tables , 1985 .

[10]  Jürgen Gauss,et al.  Coupled‐cluster methods with noniterative triple excitations for restricted open‐shell Hartree–Fock and other general single determinant reference functions. Energies and analytical gradients , 1993 .

[11]  B. Roos,et al.  On the electronic structure and spectrum of CuF2 and CuCl2 , 1998 .

[12]  D. Toohey,et al.  Chlorine Chemistry on Polar Stratospheric Cloud Particles in the Arctic Winter , 1993, Science.

[13]  M. Molina,et al.  Chemical kinetics and photochemical data for use in stratospheric modeling , 1985 .

[14]  J. Burkholder,et al.  Ultraviolet absorption spectrum of HOCl , 1993 .

[15]  Timothy J. Lee,et al.  An efficient formulation and implementation of the analytic energy gradient method to the single and double excitation coupled-cluster wave function - Application to Cl2O2 , 1991 .

[16]  S. Sander,et al.  Rate of formation of the ClO dimer in the polar stratosphere: implications for ozone loss. , 1989, Science.

[17]  F. Rowland,et al.  Bromine nitrate and its stratospheric significance , 1978 .

[18]  D. Toohey,et al.  A wintertime in situ profile of BrO between 17 and 27 km in the Arctic vortex , 1997 .

[19]  A. Wahner,et al.  Twilight variation of vertical column abundances of OClO and BrO in the north polar region , 1992 .

[20]  M. Head‐Gordon,et al.  Ab Initio Calculations of Singlet and Triplet Excited States of Chlorine Nitrate and Nitric Acid , 1995 .

[21]  D. R. Hanson,et al.  Heterogeneous chemistry of bromine species in sulfuric acid under stratospheric conditions , 1995 .

[22]  J. Orlando,et al.  Gas-Phase UV/Visible Absorption Spectra of HOBr and Br2O , 1995 .

[23]  D. Toohey,et al.  Free Radicals Within the Antarctic Vortex: The Role of CFCs in Antarctic Ozone Loss , 1991, Science.

[24]  Stephen R. Langhoff,et al.  Quantum mechanical electronic structure calculations with chemical accuracy , 1995 .

[25]  SINGLE REFERENCE COUPLED CLUSTER AND PERTURBATION THEORIES OF ELECTRONIC EXCITATION ENERGIES , 1997 .

[26]  C. Bauschlicher.  The dissociation energies of FeF, FeCl, and FeBr and their positive ions , 1996 .

[27]  Timothy J. Lee.  Ab Initio Characterization of Triatomic Bromine Molecules of Potential Interest in Stratospheric Chemistry , 1995 .

[28]  Gustavo E. Scuseria,et al.  Achieving Chemical Accuracy with Coupled-Cluster Theory , 1995 .

[29]  Manabu Oumi,et al.  A doubles correction to electronic excited states from configuration interaction in the space of single substitutions , 1994 .

[30]  H. Schaefer,et al.  Systematic study of molecular anions within the self‐consistent‐field approximation: OH−, CN−, C2H−, NH−2, and CH−3 , 1985 .

[31]  V. Kellö,et al.  Electron correlation and relativistic contributions to molecular electric properties : dipole and quadrupole moments of cyanogen halides , 1992 .

[32]  J. Crowley,et al.  Ultraviolet−Visible Absorption Cross Sections of Gaseous HOBr , 1998 .

[33]  John D. Watts,et al.  Iterative and non-iterative triple excitation corrections in coupled-cluster methods for excited electronic states: the EOM-CCSDT-3 and EOM-CCSD(T̃) methods , 1996 .

[34]  Timothy J. Lee.  Ab initio characterization of HBrO2 isomers: implications for stratospheric bromine chemistry , 1996 .

[35]  Peter R. Taylor,et al.  General contraction of Gaussian basis sets. I. Atomic natural orbitals for first‐ and second‐row atoms , 1987 .

[36]  A. Sinha,et al.  Near-Threshold Photodissociation Dynamics of HOBr: Determination of Product State Distribution, Vector Correlation, and Heat of Formation , 1996 .