The electronic ground state () of the cyclohexadienyl radical (c-C6H7) has been studied by explicitly correlated coupled clustertheory 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-staterotational constants are predicted to be A0 = 5347.3 MHz, B0 = 5249.7 MHz, and C0 = 2692.5 MHz. The calculated vibrational wavenumbers agree well with the recent p-H2 matrix IR data [M. Bahou, Y.-J. Wu, and Y.-P. Lee, J. Chem. Phys.136, 154304 (Year: 2012)10.1063/1.3703502] 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 (ν12 and ν11) by one vibrational quantum have relative intensities of more than 15%. The C6H6-H dissociation energy is calculated to be D0 = 85.7 kJ mol−1, with an estimated error of ∼2 kJ mol−1.
Received 21 September 2012Accepted 06 December 2012Published online 03 January 2013
Thanks are due to Professor Yuan-Pern Lee (Academia Sinica, Taipei, Taiwan) for providing us with the paper of Ref. 21 prior to publication.
Article outline: I. INTRODUCTION II. DETAILS OF CALCULATIONS III. RESULTS AND DISCUSSION A. Equilibrium structure, rotational constants, and dipole moment for c-C6H7 B. On the fundamental vibrations of c-C6H7 C. The adiabatic ionization energy of c-C6H7 and the first band of the PE spectrum D. The enthalpy of the reaction C6H7 → c-C6H6 + H and the heat of formation of c-C6H7 IV. CONCLUSIONS