对甲氧基苯甲腈的单色共振双光子电离光谱

对甲氧基苯甲腈是一种重要的化学化工原料,本文采用超声分子束技术和共振多光子电离方法获得了对甲氧基苯甲腈的单色共振双光子电离光谱,基态S0到电子激发态S1的0←0跃迁被确定为(35549±2)cm~(-1),结合含时密度泛函理论计算结果对观察到的光谱进行了振动模式标识和描述.实验发现呼吸振动模非常易于激活,其基频和二次泛频光谱很强,三次泛频也可明确标识,观察到大量呼吸振动与其他正则模的结合振动,这是对甲氧基苯甲腈不同于常见的多原子分子的一个重要特性.这些结果为研究对甲氧基苯甲腈的里德堡态、动力学和零动能光谱等提供了重要的参考数据.

One color resonance two-photon ionization spectra of p-methoxybenzonitrile

p-methoxybenzonitrile is an important chemical and industrial material which has been widely used in many fields, such as medicine, chemistry, photoelectron, etc. In this paper, we use the technologies of supersonic molecular beam, resonance enhanced multiphoton ionization and time-of-flight mass spectrometer to obtain the high-resolution one color resonance two-photon ionization spectra of p-methoxybenzonitrile in a vibrational wavenumber range of 0-2400 cm^-1. In order to analyze the experimental results, the theoretical calculations are performed. The molecular structure, energy, and vibration frequencies at the electronic excited state S₁ are computed with time-dependent density functional theory at the level of B3PW91/6-311 g++^**. According to the calculated results, the observed bands are assigned by the method of Varsanyi and Szoke. The band origin of the S₁←S₀ electronic transition of p-methoxybenzonitrile is determined to be (35549±2) cm^-1. A lot of vibrational bands of the electronic excited state S₁ are observed. The results show that the vibrational modes of 9b, 6b, 15 and 1 are very easy to activate in a wavenumber range of 0-800 cm^-1. There are also a lot of intense bands in a wavenumber range of 800-1600 cm^-1. In addition to the fundamental vibrations, many combined vibrations between breathing and other fundamental vibrations are found. Several vibrations in this range are located at OCH₃ and CN group. Most of the bands in a range of 1600-2400 cm^-1 correspond to ones in the range of 800-1600 cm^-1. Except for the bands appearing at 1664 and 2156 cm^-1, which are assigned to 15₀¹13₀¹ and ν(CN) (CN stretching) respectively, the remaining bands in the range of 1600-2400 cm^-1 are assigned as the combined vibrations between the breathing and the corresponding modes in the range of 800-1600 cm^-1, i.e., the combined vibrations between the breathing overtone and other fundamental modes. Our theoretical calculations show that except for CN stretching vibration at 2162 cm^-1, there is no fundamental frequency in a range of 1600-3000 cm^-1, which is consistent with our experimental result and assignment. The fundamental of the breathing vibration 1¹ and its second overtone vibration 1² are very strong. The third overtone frequency 1³ can be identified unambiguously. This is an important characteristic of p-methoxybenzonitrile, which is different from that of the usual polyatomic molecule. These results provide important reference for future researches on Rydberg states, chemical kinetics and zero kinetic energy spectroscopy of p-methoxybenzonitrile.