对氯苯腈的双色共振双光子电离和质量分辨阈值电离光谱

Two-color resonance enhanced two-photon ionization and mass analyzed threshold ionization spectroscopy of p-chlorobenzonitrile

本文利用双色共振双光子电离和质量分辨阈值电离光谱技术,研究了对氯苯腈分子第一电子激发态S_(1)和离子基态D_(0)的振动特征,确定了对氯苯腈分子S_(1)←S_(0)电子跃迁的激发能为35818±2 cm^(-1),精确的绝热电离能为76846±5 cm^(-1).对氯苯腈分子^(35)Cl和^(37)Cl两种同位素有相同的激发能和电离能以及相似的振动特征.采用高精度密度泛函方法,计算了对氯苯腈分子在中性基态S_(0)、第一电子激发态S_(1)、离子基态D_(0)的结构参数和振动频率,分析了电子激发和电离过程中对氯苯腈分子结构和振动频率的变化,并对激发态和离子基态的振动光谱进行了归属,振动光谱上的活性振动大多数是苯环平面内的弯曲振动.通过比较对氯苯酚、对氯苯胺、对氯苯甲醚、对氯苯腈与苯酚、苯胺、苯甲醚、苯腈分子的跃迁能,分析了取代基Cl原子与苯环之间的相互作用及其对分子跃迁能的影响.

The vibrational features of p-chlorobenzonitrile in its first electronically excited state S_(1) and cationic ground state D_(0) have been investigated by two-color resonance enhanced two-photon ionization and mass analyzed threshold ionization spectroscopy.The excitation energy of S_(1)←S_(0) and the ionization energy of ^(35)Cl and ^(37)Cl isotopomers of p-chlorobenzonitrile are determined to be 35818±2,and 76846±5 cm^(-1),respectively.These two isotopomers have similar vibrational features.Most of the active vibrations in the S_(1) and D_(0) states are related to the motions of the in-plane ring deformation.The stable structures and vibrational frequencies of p-chlorobenzonitrile are also calculated by the B3LYP/aug-cc-pVDZ method for the S_(0) and D_(0) states,and TD-B3LYP/aug-cc-pVDZ method for the S_(1) state.The changes in the molecular geometry are discussed in the S_(1)←S_(0) photoexcitation process and the D_(0)←S_(1) photoionization process.The comparisons between the transition energy of p-chlorophenol,p-chloroaniline,p-chloroanisole,and p-chlorobenzonitrile with those of phenol,anisole,aniline,and benzonitrile provide an insight into the substitution effect of Cl atom.