High-resolution infrared and millimeter-wave spectroscopy of CH35Cl3: The v2=v6=1 combination level

Abstract

The v2=v6 = 1 (∼936.5 cm−1) vibrational level of chloroform CH35Cl3 has been studied for the first time by high-resolution FTIR and millimeter-wave spectroscopy. Like the v6 = 1 and v3=v6 = 1 vibrations, the v2=v6 = 1 level is characterized by an exceedingly small value of |C − B − Cζ| ≈ 2.88 × 10−3 cm−1. Hence, a global l(2,2) resonance connects the (k − 1, l6 = −1) and (k + 1, l6 = +1) sublevels. This quasi-generalized l(2,2) resonance is almost exclusively responsible of the appearance of the ν2 + ν6 combination band, with its Q-branches falling in a narrow region close to the band origin, together with its, partially resolved, clusters of K-lines on the P and R sides of the spectrum, for each value of J.Despite the weakness of the ν2 + ν6 band, more than 3000 infrared transitions have been assigned, with 2 ≤ J ≤ 102 and − 84 ≤ K′′ · ΔK ≤ +89. These Fourier transform infrared data were combined with about 400 mm-wave transition frequencies in the v2=v6 = 1 state, in a simultaneous fit. The results of the least-squares calculations gave, for instance (in cm−1), ν0 = 936.507 616 1 (43), B = 0.109 702 546 5 (21), C = 0.057 000 223 3 (43), Cζ = −0.049 822 158 (74), and q22 = −6.382 793 (93) × 10−5.