Raman Spectra of Polyatomic Gases

Abstract

Raman spectra of gaseous CO2, N2O, NH3, CH4 and C2H4 have been photographed using the line λ2536 of mercury as the exciting radiation. Vibrational transitions have been observed in all the gases investigated, and rotational transitions in the cases of NH3 and CH4. For the frequency shifts due to the vibrational transitions, the following numerical values (in cm^-1) have been found: CO2: 1264.5; 1285.1; 1387.7; 1408.4. CH4: 2914.8; 3022.1; 3071.5. N2O: 1281.8 C2H4: 1342.4; 1623.3; 2880.1; 3019.3; 3240.3; 3272.3. NH3: 3333.6 Raman spectra of liquid NH3 have been photographed and found to give the two frequency shifts: 3298.4 and 3214.5. In the case of gaseous NH3, pure rotational transitions lead to a moment of inertia having the value I0=2.79×10^-40. In the case of methane, the positive and negative branches of the 3022.1 band lead to the value I0=5.17×10^-40. The relations between these data and infra-red absorption data are discussed.