Vibrational and rotational level dependence of the S1 decay of propynal in a supersonic jet

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Abstract
Single vibronic level and single rovibronic level decays of the first excited singlet state [ΔEvib (S1)≤1300 cm−1] of propynal (HCCCHO) and propynal‐d1 (HCCCDO) have been investigated in a pulsed supersonic jet. For this purpose, the emission decay rates were measured for ∼200 rotational levels in 14 vibronic bands of HCCCHO and ∼100 rotational levels in nine vibronic states of HCCCDO. The internal conversion process, which is the main deactivation route of the S1 state in HCCCHO, was found distinctly mode dependent with the ν10 vibration (CHald wagging mode) acting as the dominant promoting mode. The nonradiative decay rates showed no simple systematic dependence of the rotational quantum numbers J and K. For a number of rotational levels an oscillatory decay behavior (quantum beats) was observed the analysis of which provided information on the S1–T1 coupling in propynal.