Isotope effects in the high-resolution infrared spectrum of OC–HF

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Abstract
High-resolution infrared spectra of the H–F stretching bands of natural OC–HF and enriched O13C–HF and 18OC–HF have been recorded under thermal equilibrium conditions near 195 K with a tunable difference-frequency laser. The rotational constants of the three isotopic species are consistent with the linear C–H van der Waals bond as determined by microwave spectroscopy. The isotope shifts for the band centers exhibit a curious staggering with total CO mass which we attribute to anharmonic coupling of the zero-point CO bending motion. Resolved splittings of the l doublets in a hot band originating in the CO bending vibration yield tentative assignments and rotational constants for this low frequency van der Waals mode.