Anomalies in the pure rotation spectrum of fluoroform in excited vibrational states

Abstract

Theoretically, the K = 0 levels of a symmetric top can have only a quadratic Stark effect, but in the J = 1 ← 0 spectrum of CHF 3, the rotation lines in three of the excited vibrational states have a linear Stark effect, with displacements Δv 5 = ±0.82 × 10 −2 ϵ Mc/sec, Δv 4 = ±2.30 × 10 −2 ϵ Mc/sec, Δv 2 = ±2.16 × 10 −2 ϵ Mc/sec. No quadratic Stark effect could be detected for these lines. Their line width is only one third that of the normal lines, but the Stark lobes broaden very rapidly as the field is increased. The J = 1 ← 0 spectrum of CDF 3 is entirely normal, and the α′s were measured for five of the six fundamental vibrations. The value of α 1 for the CD stretching vibration was obtained from a high-resolution study of the ν 1 fundamental band, and therefore B e = 9999.20 Mc/sec could be obtained. In the J = 2 ← 1 spectrum of CHF 3 the ν 6, K = 0 line is displaced 14.7 Mc/sec from its expected position, and has four Stark lobes. In CDF 3, the ν 6, J = 2 ← 1, K = 0 line is split into three lines spread over 157 Mc/sec. At least two of these lines are degenerate with a linear Stark effect. This splitting is indeed puzzling, since the K = 0 levels of a degenerate vibration are of species E, and it is normally considered that these levels cannot be split by any interaction of vibration and rotation. No explanation can be offered for any of the anomalies.