Infrared spectra of N2O–4He, N2O–3He, and OCS–3He complexes

Infrared spectra of the weakly bound complexes N2O–4He, N2O–3He, and OCS–3He have been observed using a tunable diode laser to probe a pulsed supersonic jet expansion. The rotational structure of the bands was analyzed using a conventional asymmetric rotor Hamiltonian. The N2O–3He and OCS–3He spectra are mostly a type (ΔKa=0) in structure, with very weak b-type (ΔKa=±1) transitions, but for N2O–4He the a- and b-type components are both prominent. The fitted rotational parameters are consistent with roughly T-shaped structures with intermolecular separations around 3.4–3.5 Å for N2O–He and 3.8–3.9 Å for OCS–He. The angle between the N2O or OCS axis and the He position is about 80° for N2O–He and 65° for OCS–He. The vibrational band origins are slightly blueshifted from those of the free molecule, with the N2O–He shifts (+0.2 cm−1) being about twice the magnitude of the OCS–He shifts (+0.1 cm−1). The results are of particular interest since N2O and (especially) OCS have both been used as probes in experiments on ultracold helium nanodroplets.