The ground and ν6=1 vibrational levels of HC35Cl3: The first high-resolution analysis of the ν6 fundamental band

The paper reports on the first high-resolution study of the weak ν6 fundamental rovibrational band of monoisotopic chloroform HC35Cl3. More than 4500 infrared transitions pertaining to the ν6 band have been assigned, spanning the rotational states J=0-95 and −73≤KΔK≤89. The new Fourier transform infrared data were combined with accurate submillimeter-wave transition frequencies in the v6=1 state measured previously [Journal of Molecular Structure 795; 2006: 157-162] in a simultaneous fit. The existence of resonance crossings due to the Δk=±1,Δl=∓2l-type resonance in the v6=1 state, which generated perturbation-allowed rotational transitions, provided independent values of the C and Cζ6 constants. When we combined them with the wavenumbers of the fundamental ν6 band, we were able to determine accurately the axial rotational constants in the vibrational ground state C0=0.05715783 (20) cm−1, DK0=2.759 (63)10−8 cm−1, and even HK0=−8.27 (75)10−14 cm−1.

► First high-resolution study of the ν6 band of HC35Cl3, near 260 cm−1. ► Fourier-transform IR and MMW data were combined in a simultaneous fit. ► A precise value of the ν6 band center has been obtained. ► The axial ground state rotational constants were accurately determined. ► A fully quantitative reproduction of the experimental data has been achieved.