Overtone spectroscopy and dynamics in monodeuteroacetylene (C2HD)

Complementary experimental, ab initio and dynamical investigations are reported on monodeuteroacetylene, C₂HD (¹Σ⁺). All experimental spectroscopic results previously reported in the literature 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 between 4600 and 9000 cm⁻¹. The presence of numerous weak bands along the whole spectral range is analysed in terms of systematic anharmonic couplings. The entire set of energy data is then used to produce thirty-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-dimensional 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 involving an original package of computer programs is described. The evolution of the overtone intensities of the CH and CD stretches, up to η = 4, is interpreted on that basis in terms of electric and mechanical anharmonicity contributions. Eventually, dynamical aspects are studied thanks to the newly introduced vibrograms, which allow to obtain the time recurrences of the vibrational dynamics. Using the Gutzwiller and Berry-Tabor trace formulas, these vibrational recurrences are semiclassically assigned to periodic orbits of the classical Hamiltonian given by the Dunham expansion.