CARS Spectra of HCI, N₂, and C₂H₂ in the Gas Phase

Coherent anti-Stokes Raman scattering (CARS) spectra of HCl, N2, and the ν1 fundamental of C2H2 have been measured in the gas phase. The measured spectra show rotational structures which originate from the Q-branch transitions. The spectra have successfully been simulated with proper selection rules, line positions, and relative intensities from room temperature Boltzmann population distributions. The vibration-rotation interaction constant α of HCl in the ground electronic state has been measured from the rotationally resolved CARS spectra which is α=0.3076 cm-1. Possibilities of optical pumping and of measuring state specific energy distributions of molecules are discussed.