Millimeter-wave optical double resonance schemes for rapid assignment of perturbed spectra, with applications to the C̃1B2 state of SO2

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 coherenceconverted population transfer scheme for background-free mmODR, which provides a ∼10-fold sensitivity improvement over the population labeling scheme. We analyze perturbations in theC state of SO 2 , and we rotationally assign a b 2 vibrational level at 45 328 cm −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 theC state of SO 2 between 46 800 and 47 650 cm −1 . C 2015 AIP Publishing LLC. [http://dx

Observation of b2 symmetry vibrational levels of the SO2 C̃ 1B2 state: Vibrational level staggering, Coriolis interactions, and rotation-vibration constants

“…27 An apparent local perturbation in the J KaKc = 7 16 rotational level of the higher-lying b 2 vibrational level at 45328 cm −1 , with a magnitude of ∼0.4 cm −1 has also been observed. 8 However, we are unaware of local perturbations to otherC-state levels that follow similar J and K a dependence. Therefore, without additional information, we cannot with certainty invoke a specific interaction with a different electronic state.…”

The rotation-vibration structure of the SO2 C̃1B2 state explained by a new internal coordinate force field

“…However, accurate deperturbation had been impossible until the recent direct observation of b 2 vibrational levels. 25,26 In this section, we present level-specific…”

“…With direct high resolution measurements of the first eight b 2 symmetry vibrational levels, 25 and an additional b 2 level at 2754 cm −1 , 26 we can now determine a more physical and accurate force field for the SO 2 C1 B 2 state. The accuracy of the force field of Hoy and Brand is limited by the reduced-dimension nature of their fit, and the fact that the ν 3 fundamental level, the position of which was estimated from the inferred position of the (0,1,1) level, 11 was the only b 2 symmetry level included in the fit.…”

“…This uncertainty is sufficiently large that it precludes determination of the number of quanta of excitation in ν 2 . Recently, we implemented the Coherence-Converted Population Transfer technique 31 in a sensitive, background-free scheme for millimeter-wave optical double resonance (CCPT-MODR)26 to probe the vibrational levels near the 2762 cm −1 state, including one dark b 2 symmetry level, which borrows intensity via the Coriolis interaction. We assigned 16 rotational levels of the dark b 2 symmetry level (as well as many additional rotational levels of the 2762 cm −1 state and 4 rotational levels of an a 1 symmetry level at 2743 cm −1 ).…”

Final State Resolved Quantum Predissociation Dynamics of SO2(C̃1B2) and Its Isotopomers via a Crossing with a Singlet Repulsive State

“…[21][22][23] The spectroscopy of this so-called C band has been extensively studied in the past, and a plethora of spectroscopic data exist above the band origin at 42573 cm -1 . [24][25][26][27] Above 218 nm, SO2 is known to predissociate, as evidenced by a sudden decrease of fluorescence and broadening of the spectral features. 21,24,[28][29][30][31][32][33] The dissociation dynamics to the SO( 3 X   ) and O( 3 P) species has been studied by a number of groups, using different experimental techniques.…”