HIGH-RESOLUTION INFRARED STUDY OF THE NU(5) BAND OF CH2=CHF BY DIODE-LASER SPECTROSCOPY

The infrared spectrum of the ν5 fundamental of CH2CHF has been investigated in the range 1334-1404 cm-1 with a resolution of ca. 0.002 cm-1 using a tunable diode laser spectrometer. This vibration of symmetry species A′ gives rise to an a/b hybrid band exhibiting patterns characteristic of molecules approaching the prolate symmetric-top limit. The J fine structure has been resolved in several (P, Q, R)QK clusters, and the rovibrational analysis in the P, Q, and R branches has led to the assignment of more than 1100 lines with J ≤ 45 and Ka ≤ 11. The band is affected by different Coriolis-type resonances and nearby states such as ν8 + ν9, ν9 + ν10, and ν9 + ν11 seem to be involved in the interactions; the perturbation effects have been found to be stronger for the K′a = 9 and 10 levels. Using Watson′s A-reduction Hamiltonian in the Ir representation, a least-squares fit of about 900 transitions, free of major resonance contribution, provided a set of effective molecular constants for the v5 = 1 state of CH2CHF. © 1993 Academic Press, Inc.