Pure Rotational Raman Spectra of ⁷⁹ Br ₂ and ⁸¹ Br ₂

The pure rotational Raman spectra of the lighter halogen molecules have been studied by several authors. Andrychuk, Claassen et al., Stricker and Hochenbleicher, and Edwards et al., reported the spectra of fluorine, whereas Hochenbleicher and Schrotter and Hendra and Vear were able to record the pure rotational Raman spectrum of chlorine. Accurate values of the rotational constant B0 have been obtained for these molecules. However, because of the low value of B0 the pure rotational Raman spectrum of the heavier halogen molecules could not be resolved until now. In the course of an extensive resonance Raman spectroscopic study on natural bromine (which is a mixture of the molecules 79Br2, 79Br81Br and 81Br2) as well as on the isotopically pure molecules 79Br2 and 81Br2, we have also studied the rotational Raman spectra of the isotopically pure species 79Br2 and 81Br2. The results will be presented in this note, where it is shown that the pure rotational Raman spectra of fairly heavy linear molecules can be obtained directly with photoelectric recording.