Rotational Raman scattering in the instructional laboratory

Abstract

We describe the use of a single spectrometer and a low power argon laser for the study of the pure rotational Raman spectra of H2, O2, N2, and CO2. Analyses of the spectra allow the student to obtain internuclear separations in the ground state, the rotational temperature of the gas, and the influence of nuclear spin on the allowed rotational states. The four molecules chosen for study have nuclei with spins of I=0 (O2), 1/2 (H2), and 1 (N2) and thus the discussion includes the effects of both Bose and Fermi exchange properties on the symmetry of the overall wave function. To fully illustrate the range of information available from the data, we provide spectra obtained with a high quality double spectrometer which allow even the lowest rotational states to be observed and show the stretching of the H2 molecule due to centripetal forces.