A vibronic level study of the spectroscopy and photophysics of the C6H6–CHCl3 complex has been
carried out using a combination of laser-induced fluorescence and resonant two-photon ionization (R2PI).
In C6H6-CHCl3, the S1–S0 origin remains forbidden while the 1610 transition is weakly induced. Neither
610 nor 1610 are split by the presence of the CHCl3 molecule. On this basis, a C3vstructure is deduced
for the complex, placing CHCl3 on the six-fold axis of benzene. The large blue-shift of the complex’s
absorption relative to benzene (+178 cm–1) and the efficient fragmentation of the complex following
one-color R2PI reflect a hydrogen-bonded orientation for CHCl3 relative to benzene’ π
cloud. Dispersed
fluorescence scans place a firm upper bound on the ground state binding energy of the complex of
2,024 cm–1. Both the 61and 61 11 levels do not dissociate on the time-scale of the S1 fluorescence and
show evidence of extensive state mixing with van der Waals’ levels primarily built on the 00 level of
benzene. The C6H6–(CHCl3)2 cluster shows extensive intermolecular structure beginning at +84 cm–1, a
strong origin transition, and splitting of 61. A structure which places both CHCl3 molecules on the same
side of the benzene ring is suggested on this basis. The vibronic level scheme used to deduce the structure
of C6H6–CHCl3 is tested against previous data on other C6H6–X complexes. The scheme is found to be
capable, in favorable cases, of deducing the structures of C6H6–X complexes based purely on vibronic
level data. Finally, the results on C6H6–CHCl3 are compared with those on C6H6–HCl and C6H6-H2O to evaluate the characteristics of the n hydrogen bond.
