OVERTONE SPECTROSCOPY AND DYNAMICS IN MONODEUTEROACETYLENE (C2HD)

Complementary experimental, ab initio and dynamical investigations are reported on monodeuteroacetylene, C2HD((X) over tilde(1) Sigma(+)). A ll experimental spectroscopic results previously reported in the liter ature on C2HD, i.e. from 500 to 16000 cm(-1) are gathered. New results are included, which are obtained from the analysis of absorption data recorded with a Fourier transform interferometer at high resolution b etween 4600 and 9000 cm(-1). The presence of numerous weak bands along the whole spectral range is analysed in terms of systematic anharmoni c couplings. The entire set of energy data is then used to produce thi rty-five vibrational frequencies and anharmonicities from a fit of the vibrational energies to a Dunham-type expansion, and the vibrational level density is extrapolated, up to higher energy, One- and two-dimen sional potential energy and dipole moment surfaces refined from new ab initio results are fitted to a selected set among those experimental data, associated to the stretch overtones. The iterative procedure inv olving an original package of computer programs is described. The evol ution of the overtone intensities of the CH and CD stretches,up to ups ilon = 4, is interpreted on that basis in terms of electric and mechan ical anharmonicity contributions. Eventually, dynamical aspects are st udied thanks to the newly introduced vibrograms, which allow to obtain the time recurrences of the vibrational dynamics. Using the Gutzwille r and Berry-Tabor trace formulas, these vibrational recurrences are se miclassically assigned to periodic orbits of the classical Hamiltonian given by the Dunham expansion.