Millimeter-wave absorption spectroscopy combined with a pulsed jet expansion technique was applied to measure the internal rotation j = 2-1 hot band of the Ar-HCN complex in the frequency region of 147-287 GHz. In total 153 rovibrational lines, split into hyperfine components due to the nitrogen nucleus, were assigned to the ∑2-∑1, ∑ 2-Π1, Π2-∑1, Π 2-Π1, Δ2-∑1, and Δ2-Π1 subbands. A set of molecular constants for the ∑2, Π2, and Δ2 internal rotation substates, including subband origins, rotational constants, nuclear quadrupole coupling constants, and Coriolis interaction constants, was determined. The internal rotation energy for the Σ2 state, 412.8949 GHz, is higher than those for the Π2 and Δ 2 states, 392.3974 and 355.9570 GHz, by 20.498 and 56.938 GHz, respectively, in contrast to the ∑1 state located by 17.094 GHz lower than the Π1 state, the anisotropy of potential energy surface affecting the j = 2 and j = 1 states differently. The rotational and quadrupole coupling constants in the j = 2 excited state are quite different from those in the ground state, indicating drastic change in the average structure in the j = 2 state from the ground state. The determined molecular constants were compared with those calculated from the potential energy surface computed at the CCSD(T) level.
All Science Journal Classification (ASJC) codes
- Atomic and Molecular Physics, and Optics
- Physical and Theoretical Chemistry