Infrared photodissociation spectra of the C-H stretch vibrations of C6H6+-Ar, C6H6+-N2, and C6H6+-(CH4)1-4

Vibrational infrared photodissociation spectra of mass selected C6H6+-Ar, C6H6+-N-2, and C6H6+-(CH4)(1-4) ionic complexes are recorded in the spectral range of the C-H stretching vibrations. Transitions at 3095 +/- 15 cm(-1) occur in all spectra and are assigned to C-H stretch fundamentals of the benzene cation in its E-2(1g) electronic ground state. In the case of the C6H6+-(CH4)(1-4) complexes, additional transitions at 2904 +/- 7 and 3010 +/- 24 cm(-1) are observed and attributed to the symmetric and antisymmetric C-H stretch vibrations of the CH4 ligands, nu(1) and nu(3). The deduced C-H stretching vibrations of C6H6+ in the E-2(1g) ground state are roughly 30 cm(-1) higher than the corresponding frequencies in the (1)A(1g) electronic ground state of the neutral species, indicating that the C-H bonds become stronger upon removal of an electron from the highest occupied e(1g) orbital of C6H6. (C) 1999 American Institute of Physics. [S0021-9606(99)01648-7].