High-resolution infrared spectrum and analysis of the ν1 band of CF337Cl

The rotational structure of CF₃³⁷Cl ν₁ band has been investigated using spectra of trifluorochloromethane in natural isotopic abundance, recorded with a tunable diode laser spectrometer. The spectra analyzed have been obtained by keeping the sample at low temperature (～200 K) to minimize the strong interference arising from “hot” band transitions. The K structure of many P(J) and R(J) multiplets has been resolved and positively identified: the maximum J value reached in the P and R branches was 38 and 40, respectively. About 650 unblended lines have been used for the least-squares fit to the energy expression including the quartic centrifugal distortion coefficients. Molecular constants for the ν₁ band of CF₃³⁷Cl have been derived. A weak perturbation affecting the rotational levels with K = 18 and J′ ≥ 36 has also been observed.