Excited vibrational states of benzene: High resolution FTIR spectra and analysis of some out-of-plane vibrational fundamentals of C6H5D Original Research Article

We have measured the infrared spectra of the ν4, ν10b and ν11 fundamental bands of C6H5D in the range 540–830 cm−1 with an instrumental bandwidth of 0.0024 cm−1 (unapodized FWHM) using a Bomem DA 002 Interferometric Fourier Transform spectrometer. The rotational analysis for ν4 yields ground state constants by combining ground state combination differences and published microwave data (M. Oldani and A. Bauder, Chem. Phys. Lett. 108 (1984) 7). Excited state constants for the ν4 level were obtained up to quartic terms, using Watsonʹs A-reduction Hamiltonian in the IIIr representation, resulting in a band center ν̃40=697.593 cm−1. A partial analysis is presented for the ν10b fundamental (ν̃10b0=778.027 cm−1), which appears to be locally perturbed by the ν16a+ν16b combination band. The very strong ν11 band is strongly perturbed, most probably by ν6a and ν6b. The results are discussed in relation to comparison with accurate ab initio electronic structure calculations including non Born-Oppenheimer effects as well as potential applications with isotope tracer detection and infrared laser chemistry.