Low frequency vibrational anharmonicity and nuclear spin effects of Cl-(H2) and Cl-(D2)

Low frequency combination bands of Cl-35(-)(H-2) and Cl-35(-)(D-2) 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 Cl-35(-)(H-2) (Cl-35(-)(D-2)) 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 v(1) + v(2), 2v(1) + v(2), and 3v(1) + v(2) for Cl-35(-)(H-2) and 2v(1) + v(2), 3v(1) + v(2), and 4v(1) + v(2) for Cl-35(-)(D-2), where v(1) is the Cl-35(-) ... H-2 stretching fundamental and v(2) is the Cl-(H-2) bend. The observed asymmetric temperature dependent line shape of the v(1) + v(2) transition can be modeled by a series of Sigma(+)-Pi ro-vibrational transitions, when substantially decreasing the rotational constant in the vibrationally excited state by 35%. The spectrum of Cl-35(-)(D-2) shows a splitting of 7 cm(-1) for the strongest band which can be attributed to the tunneling of the ortho/para states of D-2. (c) 2018 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license.