Journal
MOLECULAR PHYSICS
Volume 117, Issue 21, Pages 3011-3026Publisher
TAYLOR & FRANCIS LTD
DOI: 10.1080/00268976.2018.1554865
Keywords
LIF; 2D-LIF; fluorescence excitation; dispersed fluorescence; torsions
Funding
- EPSRC [EP/L021366/1, 1934851] Funding Source: UKRI
- Engineering and Physical Sciences Research Council [1934851] Funding Source: researchfish
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Two-dimensional laser-induced fluorescence (2D-LIF) spectroscopy is employed to identify contributions to fluorescence excitation spectra that arise from both overlapping bands and coupling between zero-order states (ZOSs). Evidence is found for the role of torsional motion in facilitating the coupling between vibrations that particularly involves the lowest-wavenumber out-of-plane vibrational modes. The experiments are carried out on jet-cooled p-fluorotoluene, where the molecules are initially in the lowest two torsional levels. Here we concentrate on the 390-420 cm(-1) features in the S-1 <- S-0 excitation spectrum, assigning the features seen in the 2D-LIF spectrum, aided by separate dispersed fluorescence spectra. The 2D-LIF spectra allow the overlapping contributions to be cleanly separated, including some that arise from vibrational-torsional coupling. Various coupling routes open up because of the different symmetries of the lowest two torsional modes; these combine with the vibrational symmetry to provide new symmetry-allowed vibration-torsion ('vibtor') interactions, and the role of the excited m = 1 torsional level is found to be significant.
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