Abstract
A deceptively simple feature in the S1 ← S0 spectrum of p-fluorotoluene (pFT), 1013 cm-1 above the origin, is studied using both zero-electron-kinetic-energy (ZEKE) and two-dimensional laser-induced fluorescence (2D-LIF) spectroscopy. It is found to consist of a cornucopia of overlapped transitions to eigenstates that arise from numerous interacting levels. A significant variation in the activity is seen employing both the ZEKE and 2D-LIF techniques. Detailed insight into the complicated spectra can be achieved, owing to the large number of vibrational wavenumbers that have been previously determined for the S0, S1, and D0 + states, summarized herein. It is found that the activity is dominated by two overtones, which are individually interacting with other levels, so providing largely independent routes for vibrational energy flow at the same internal energy. Additionally, other weak features located 900-1050 cm-1 above the origin are examined.
Highlights
When chemical bonds are formed or broken, excess energy is often deposited locally; photoabsorption, photoemission, collision, internal conversion, and intersystem crossing can all lead to high amounts of vibrational energy, which again can be localized in a molecule
We concentrate on the feature that appears at 1013 cm−1 above the origin in the S1 ← S0 spectrum of pFT, but we examine a number of weak bands that lie in the range 900–1050 cm−1, identified using resonance-enhanced multiphoton ionization (REMPI)
The latter produced some interference with the pFT spectra at particular positions, and these could be straightforwardly identified from ongoing work on mFT, we refrain from presenting these 2D-LIF and DF spectra and just report on the main pFT fluorescence activity and assignments, alongside those of the ZEKE spectra
Summary
When chemical bonds are formed or broken, excess energy is often deposited locally; photoabsorption, photoemission, collision, internal conversion, and intersystem crossing can all lead to high amounts of vibrational energy, which again can be localized in a molecule What happens to this energy is of key importance in understanding the subsequent stability and reactivity of the excited molecule: this is the area of vibrational energy redistribution.[1] Understanding the details of such couplings at high internal energy is nigh on impossible, owing to the enormous numbers of coupled levels; at low internal energy such couplings can be surprisingly complicated, this is a more tractable problem. The 1013 cm−1 feature looks like a simple band, albeit broadened, it originates from a surprising number of overlapping transitions, involving eigenstates that arise from a number of interacting levels
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