Pure Rotation Spectrum of the HCl Flame

Pure rotation lines for j=17 to 33 of the emission spectrum of the HCl flame are measured with a KBr prism. The following empirical formulae are determined to represent two series of lines measured corresponding to pure rotation in the two lowest oscillation states, N=0, ν=20.9j-0.00185j³; N=1, ν=20.2j-0.00163j³.The linear coefficients agree satisfactorily with values calculated from the empirical oscillation-rotation formula. Theoretically the two cubic coefficients should be equal. The frequency is strongly influenced by the cubic term for high values of j so that the observed difference between these coefficients is regarded as real.