Spectroscopic and thermochemical properties of the c-C6H7 radical: A high-level theoretical study

Abstract

The electronic ground state ((X) over tilde B-2(1)) of the cyclohexadienyl radical (c-C6H7) has been studied by explicitly correlated coupled cluster theory at the RCCSD(T)-F12x (x = a, b) level, partly in combination with the double-hybrid density functional method B2PLYP. An accurate equilibrium structure has been established and the ground-state rotational constants are predicted to be A(0) = 5347.3 MHz, B-0 = 5249.7 MHz, and C-0 = 2692.5 MHz. The calculated vibrational wavenumbers agree well with the recent p-H-2 matrix IR data [M. Bahou, Y.-J. Wu, and Y.-P. Lee, J. Chem. Phys. 136, 154304 (2012)] and several predictions have been made. A low value of 6.803 +/- 0.005 eV is predicted for the adiabatic ionization energy of c-C6H7. Owing to a moderately large change in the equilibrium structure upon ionization, the first band of the photoelectron spectrum is dominated by the adiabatic peak (100%) and only the peaks corresponding to excitation of the two lowest totally symmetric vibrations (nu(12) and nu(11)) by one vibrational quantum have relative intensities of more than 15%. The C6H6-H dissociation energy is calculated to be D-0 = 85.7 kJ mol(-1), with an estimated error of similar to 2 kJ mol(-1). (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4773015]