The vibrational spectrum of deuterated phosphaethyne: A quantum mechanical, classical, and semiclassical analysis

Abstract

The vibrational spectrum of deuterated phosphaethyne (DCP) is analyzed in terms of quantum-mechanical variational calculations, classical mechanics (periodic orbits), and an effective Hamiltonian model. The quantum mechanical and classical calculations are performed with a new, spectroscopically accurate potential energy surface. The spectrum is governed by a 2 : 1 DC stretch : CP stretch anharmonic resonance, which already exists for the fundamentals. The bending degree of freedom is to a large extent decoupled. It is shown that several bifurcations in the classical phase space profoundly influence the quantum spectrum. For example, a new progression, which does not exist at very low excitation energies, comes into existence at intermediate energies. In contrast to HCP, the pure bending states gradually evolve along the isomerization path with increasing bending quantum number.