Fluorescence lifetimes and predissociation processes in the B̃2A′ state of CCH

Whe Yi Chiang, Yen Chu Hsu

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6 Scopus citations


Fluorescence lifetimes have been measured under supersonic jet conditions for various N, K-rotational levels of three vibrational levels (T, T + v2, and T + v3) of the B̃2A′ state of CCH. It was found that the lifetimes of levels T + v2 and T + v3 are significantly shorter than that of level T. Furthermore, the lifetimes vary in a complicated way from one rovibronic level to another, indicating the presence of local perturbations. The previously reported CC-H bond energy ranges from 95.6 to 116.3 kcal/mol, which leads to a large uncertainty in assigning the onset of the dissociation process, CCH (X̃2+)→C2(X 1g+) + H(2S1/2). In this work, fluorescence excitation spectra of photofragment C2 via D 1∑←X1g+ and d 3Πg←a 3Πu have been recorded to determine the predissociation processes of the B̃ state. Assuming no barrier is present in the dissociation process of the X and A states, the upper bound of D00(CC-H) was estimated as 39 388±7 cm-1(≃112.62kcal/mol). Hence, the lifetime quenching phenomenon observed in the B state is primarily due to predissociation via the dissociative continuum of either the X̃ or the à state of CCH.

Original languageEnglish
Pages (from-to)7394-7399
Number of pages6
JournalJournal of Chemical Physics
Issue number17
StatePublished - 1 May 2000


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