利用脉冲分子束技术,在305-322 nm范围内研究了1-萘酚(1NP)的共振双光子电离(R2PI)光谱.1NP分子存在cis和trans两种旋转异构体,但实验中仅观测到trans异构体的电子振动跃迁光谱,其S1←S0跃迁的(0-0)带头出现在317.90 nm(即31456 cm~(-1))位置.利用光谱选律及ab initio和密度泛函(DFT)计算,对trans异构体在S1态的振动模进行标识,得出主要对应于对称性为α'的半面内振动模.计算显示,cis括异构体在电子基态S0的能量较trans异构体高出439 cm~(-1),而第一激发能却比trans异构体的低1216 cm~(-1),与之相应的实验值分别是220和274 cm~(-1).计算数值与实验结果在能量变化趋势上完全一致.共振双光子电离谱中没有观测到cis异构体的光谱信号,其原因可归结为分子柬的有效冷却效应使得处于基态的cis异构体的布居数密度相对trans异构体极低,导致cis光谱信号太小而未能被探测到.%The resonant two-photon ionization (R2PI) spectrum of 1-naphthol (INP) was studied from 305 to 322 nm using supersonic molecular beam technique. 1NP has two rotamers: cis and trans. The R2PI spectrum was used to characterize the S_1←S_0 transition of the trans species and its original band appeared at 317.8 nm (31456 cm~(-1)). The vibrational bands of the trans species from the R2PI spectrum can be assigned to in-plane vibrational modes with a' symmetry. Ab initio and density functional theory (DFT) calculations indicate that the cis rotamer has higher energy than the trans rotamer by 439 cm~(-1) in the ground state but it has a lower exciting energy than the trans rotamer by 1216 cm~(-1) for the S_1←S_0 transition. These calculated results are in good agreement with the experimental trend where the difference between the cis and trans energies in the S_0 state is 220 cm~(-1) and the difference between the cis and trans exciting energies is 274 cm~(-1). There are no spectral features from the cis rotamer in the R2PI spectrum and we attribute this to the efficient cooling conditions in the molecular beam, which leads to a very small cis rotamer population with the higher energy (220 cm~(-1)).
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