HINDERED ROTATION IN ION-NEUTRAL MOLECULAR-COMPLEXES - THE NU(1) VIBRATION OF H-2-HCO-2-DCO+( AND D)

Infrared spectra of the mass selected ionic complexes H-2-HCO+ and D-2 -DCO+ have been recorded in the vicinity of their nu(1) vibrations (H- 2/D-2 stretch) by means of photofragmentation spectroscopy. The anomal ous rotational constants obtained by fitting the observed line positio ns to a semirigid Watson A-type Hamiltonian reflect the appreciable ze ro-point excursions of the H-2/D-2 molecule. Barriers for this interna l motion are estimated utilizing a simple atom-diatom hindered rotor H amiltonian. According to this one-dimensional model, the barrier incre ases by about 15% upon vibrational excitation which is mainly attribut ed to electrostatic effects. (C) 1997 American Institute of Physics. [ S0021-9606(97)00344-9].