Characteristics of low resolution Q-branch microwave bands: Applications to 2,2,2-trifluoroethyl vinyl ether and 7-methylbicyclo[2.2.1]-hept-2-ene-5-one

Abstract

A rigid rotor analysis of μb- and μc-type Q-branch series indicates overlapping low J transitions giving rise to the low resolution microwave bands which follow a half-integer frequency rule. At higher J values certain Q-branch series form bandheads shifted to a lower frequency from the series origin. Under favorable circumstances low resolution bands are expected and the frequency of these bands may be used to estimate the rotational constant parameter (A−C). The microwave spectrum of 2,2,2-trifluoroethyl vinyl ether exhibits bands which are assigned to the bandhead phenomenon. This provides a value of (A−C) and in conjunction with previous data yields the three rotational constants A, B, and C uniquely from low resolution data. The results are consistent with the s-cis-planar as well as gauche conformations. Previously reported low resolution bands of 7-methylbicyclo[2.2.1]-hept-2-ene-5-one are interpreted as two half-integer band series arising from low-lying vibrational states with slightly different values of (2A−B−C).