Study on X-H(X=C,O or N) stretching vibration of electronically excited aromatic molecules and their clusters

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The X-H(X=C,O or N) stretching vibrations of electronically excited aromatic molecules and their clusters have been investigated in supersonic jets. To observe those vibrations, new type of double-resonance spectroscopic technique has been developed, so called UV-IR double resonance spectroscopy. The systems investigated are the CH stretching vibration of benzene, toluene, the OH stretching vibration of naphthol and the NH stretching vibration of aniline in their S_1 state. Also investigated are the vibrations of their clusters. For benzene and toluene, we found that the aromatic CH stretching frequencies increase,'while those of methyl group decrease in S_1.For aniline, we found the NH stretching frequency decreases as large as 500 cm-1 in S_1. In addition, new electronically excited state has been found to locate 3200 cm^<-1> above S_1. The newly found state (S_2) is thought to be the πσ^* state.The OH stretching vibration of the H-bonded cluster of phenol has been also observed. It was found that the clusters excited to the H-bonded OH stretching vibration immediately relax, which is followed by the dissociation of the H-bond.