Microwave spectrum of formaldehyde in vibrationally excited states

Abstract

Thorough sweeps of the spectral lines of H 2CO and D 2CO in the frequency region from 8000 Mc/sec to 36000 Mc/sec have been made at room temperature as well as at 200°C. The K-type doubling lines of these molecules in the first excited states of ν 2 (CO stretching), ν 3 (HCH angle deformation), ν 5 (CH 2 in-plane bending) and ν 6 (CH 2 out-of-plane bending) vibrations with K = 1 and K = 2 have been assigned. The spectral lines of the 1 01←0 00 transitions of these excited states which appear in the millimeter wave region have been also observed. By fitting these observed lines to the asymmetric rotor energy levels, the effective rotational constants of formaldehyde in the excited states have been determined. The observed inertia defects of the excited states agreed fairly well with the theoretical values. The excited state lines could not always be fitted to the asymmetric rotor energy levels because of the strong vibration-rotation interaction. The effect of strong Coriolis interaction on the frequencies of the K-type doubling lines is discussed.