Millimeter-wave optical double resonance schemes for rapid assignment of perturbed spectra, with applications to the [~ over C] [superscript 1]B[subscript 2] state of SO[subscript 2]

Abstract

Millimeter-wave detected, millimeter-wave optical double resonance (mmODR) spectroscopy is a powerful tool for the analysis of dense, complicated regions in the optical spectra of small molecules. The availability of cavity-free microwave and millimeter wave spectrometers with frequency-agile generation and detection of radiation (required for chirped-pulse Fourier-transform spectroscopy) opens up new schemes for double resonance experiments. We demonstrate a multiplexed population labeling scheme for rapid acquisition of double resonance spectra, probing multiple rotational transitions simultaneously. We also demonstrate a millimeter-wave implementation of the coherence-converted population transfer scheme for background-free mmODR, which provides a ∼10-fold sensitivity improvement over the population labeling scheme. We analyze perturbations in the [~ over C] state of SO[subscript 2], and we rotationally assign a b[subscript 2] vibrational level at 45 328 cm[superscript −1] that borrows intensity via a c-axis Coriolis interaction. We also demonstrate the effectiveness of our multiplexed mmODR scheme for rapid acquisition and assignment of three predissociated vibrational levels of the [~ over C] state of SO[subscript 2] between 46 800 and 47 650 cm[superscript −1].