Chemical timing 4. The rovibronic level structure associated with intramolecular vibrational redistribution in S1 p-difluorobenzene

Abstract

The method of chemical timing for obtaining picosecond time-resolved fluorescence spectra has been applied to the measurement of intramolecular vibrational redistribution (IVR) in S1 p-difluorobenzene. In this report, a more detailed examination of the spectroscopy of some vibrationally mixed levels is used in conjunction with the previously measured IVR parameters to construct a generalized picture of the rovibronic level structure giving rise to IVR. Strong, off-resonance interactions are observed to mix levels separated by several cm−1, contributing additional discrete structure to the spectrum but not directly affecting the IVR dynamics. The dynamics, instead, reflect on-resonance interactions between levels separated only by a few tenths of a wave number that give rise to congested background emission. Evidence is seen in comparisons between bulb and jet spectra for the involvement of vibration-rotation coupling in both the off-resonance and the on-resonance interactions. A particularly important and subtle rotational effect is the change of the coupled vibrational field with rotational excitation due to the variation of rotational constants with vibrational excitation, leading to a smoother congested background.

Observation of Coriolis Coupling between ν2 + 4ν4 and 7ν4 in Acetylene X̃1Σ+g by Stimulated Emission Pumping Spectroscopy

“…Levels with f-parity can be reached by a Q-branch PUMP from the zero-point vibrational level followed by a Por R-branch DUMP. From an excited state level with KЈ a ϭ 1 and f-parity, only transitions to an f-parity level with lЉ ϭ 2 would be expected in the P and R branches of the 2 two transitions are seen in the top spectrum in Fig. 3 which presents the P-branch region of the Q(11)-pumped spectrum.…”

Complex and Sustained Quantum Beating Patterns in a Classic IVR System: The 3151 Level in S1 p-Difluorobenzene

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14] Among the levels studied, one found at 2068 cm -1 above the S 1 origin has attracted particular interest. [10][11][12][13] This level is usually labelled the 3 1 5 1 level, 15 and involves excitation of one quantum in mode 3 (CF stretching) and one quantum in mode 5 (ring breathing).…”

Applications of Fourier transform microwave (FTMW) detected infrared–microwave double-resonance spectroscopy to problems in vibrational dynamics

“…By monitoring a single pure rotational transition it is possible to obtain the vibrational spectrum of a single molecular species without spectral overlap from other molecules in the molecular beam. This ability to ''tag'' a single species gives this technique many of the advantages found in fluorescence, ionization dip, and rotational coherence methods [33][34][35][36][37]. Compared to ionization detection methods, the FTMW technique makes it possible to unambiguously distinguish between structural and conformational isomers.…”