The pure rotational Raman spectra of furan and cyclopentene

Abstract

The pure rotational Raman spectra of furan and cyclopentene were photographed with a plane grating spectrograph in the thirteenth order of a 300 grooves/mm blazed grating using the line Hg 4358 Å for excitation. The spectra resemble those of a symmetric top rotor with well developed R- and S-branches. The analysis of the spectra is based on the theory of the nonrigid symmetric top rotor and yields the following molecular constants. For furan, B 0 = 1 2 (A 0 + B 0) = 0.31154 ± 0.00006 cm −1 and D J = (12.5 ± 2.5) × 10 −8, cm −1; for cyclopentene, B ̃ 0 = 1 2 (A 0 + B 0) = 0.24165 ± 0.00005 cm −1 and D J = (3.75 ± 1.25) × 10 −8, cm −1. The B ̃ 0 values are in fair agreement with those calculated from microwave data. The D J -value has not been reported previously for furan. For cyclopentene, the D J -value deduced from the Raman data shows that there are no extraordinary centrifugal distortion effects, in contrast to the conclusions derived from the analysis of the microwave rotation spectrum.