The Raman Spectra of the Isotopic Molecules H2, HD, and D2

The Raman spectra of H2, HD and D2 gases, at 3 atmospheres pressure, were excited by Hg 2537 and photographed with a high dispersion quartz prism spectrograph. A total of 42 lines were analyzed. The positions of the pure rotation lines for H2 agree with the measurements of Rasetti but the lines in the Q vibration band do not. New vibrational constants calculated from the Raman and emission spectrum data of H2 and HD give calculated values of the positions of the rotational-vibration Raman lines in good agreement with the values observed for the three isotopic molecules. Contrary to the theoretical predictions, the 0,0 line of the Q vibrational band of HD was observed. A source of error in Raman measurements, namely, the movement of the spectrum due to variations of the barometric pressure during the exposure of a plate, was detected and eliminated.