Low frequency vibrational anharmonicity and nuclear spin effects of Cl-(H-2) and Cl-(D-2)

Low frequency combination bands of 35Cl–(H2) and 35Cl–(D2) have been measured in the region between 600 and 1100 cm−1 by infrared predissociation spectroscopy in a cryogenic 22-pole ion trap using a free electron laser at the FELIX Laboratory as a tunable light source. The 35Cl–(H2) (35Cl–(D2)) spectrum contains three bands at 773 cm−1 (620 cm−1), 889 cm−1 (692 cm−1), and 978 cm−1 (750 cm−1) with decreasing intensity toward higher photon energies. Comparison of the experimentally determined transition frequencies with anharmonic vibrational self-consistent field and vibrational configuration interaction calculations suggests the assignment of the combination bands v1 + v2, 2v1 + v2, and 3v1 + v2 for 35Cl–(H2) and 2v1 + v2, 3v1 + v2, and 4v1 + v2 for 35Cl–(D2), where v1 is the 35Cl–⋯H2 stretching fundamental and v2 is the Cl–(H2) bend. The observed asymmetric temperature dependent line shape of the v1 + v2 transition can be modeled by a series of ∑+-∏ ro-vibrational transitions, when substantially decreasi...