High resolution rotational CARS spectrum of oxygen

Abstract

A low frequency, high resolution CARS spectrometer is described which has been used to resolve the closely spaced Δ N = 2, Δ J = 2 triplets of oxygen in the pure rotational Raman spectrum. The transition frequencies and intensities from N = 1–19 are extracted from the experimental data with the aid of spectral simulation routines that account for the ∥χ∥ 2 interference effects and the contribution of various line broadening mechanisms to the CARS spectrum. The frequencies match well those predicted using molecular constants obtained from magnetic dipole microwave studies and a Hamiltonian appropriate to a coupling scheme intermediate between Hund's cases (a) and (b). A small, systematic discrepancy is observed between experimental and theoretical intensities which may result from a J dependent linewidth variation within each triplet.