利用静电场中光电离效率谱精确确定1,3-二乙氧基苯分子的电离能

Accurate determination of ionization energy of 1,3-diethoxybenzene via photoionization efficiency spectrum in electrostatic field

电离能是原子和分子的重要的特性参数,在光物理和光化学过程中起着重要作用,精确电离能对相关研究具有重要意义.电离能是调试零动能光谱信号的重要参考数据,在判断异构物数量和分子构型方面也起着关键作用.1,3-二乙氧基苯是一种重要的苯的衍生物,实验证实在超声分子束中包含两种旋转异构物Ⅰ(downup)和Ⅲ(down-down).它们的精确电离能还未见文献报道.本文采用直线式飞行时间质谱仪测量了静电场中1,3-二乙氧基苯光电离效率曲线,通过不同电场强度下测量的电离能(Stark效应)对场强的平方根线性拟合给出了两种异构物Ⅰ和Ⅲ精确的电离能分别为(62419±2)cm^(–1)和(63378±2)cm^(–1).相对于通常的脉冲电场加速机制和零动能光谱测量的电离能,精确度大约分别由(±10)cm^(–1)和(±5)cm^(–1)提高到(±2)cm^(–1).分析和讨论了不同方法测量的物理机制和优缺点.

Ionization energy(IE)is an important characteristic parameter of atoms or molecules.It plays an important role in the process of photophysics and photochemistry.The precise ionization energy is very important for relevant research.Especially,it is very useful for adjusting the signal of the zero-kinetic energy(ZEKE)spectrum,and it also plays a key role in judging the number of rotamers and molecular configuration.In linear time-of-flight mass spectrometers,pulsed electric fields are usually used to drive photo-ionized ions to the detector to produce the photoionization efficiency(PIE)spectrum.The ionization energy is directly obtained from the PIE curve.The uncertainty of the measured IE is usually greater than or equal to±10 cm^(–1).The ZEKE spectroscopy is based on the long-lived Rydberg state field ionization technology.In the ZEKE experiments,the laser excites molecules to the Rydberg state and then a pulsed field ionization(PFI)is used for measurement.A peak with high signal-to-noise ratio and narrow linewidth signal appears near the ionization threshold.Therefore,the more accurate ionization energy can be obtained,and the uncertainty of the measured value is about±5 cm^(–1).The 1,3-diethoxybenzene is an important benzene derivative,and experiments have confirmed that there are two rotamers,i.e.Ⅰ(down-up)and Ⅲ(down-down)in the supersonic molecular beam.In this paper,a linear time-of-flight mass spectrometer is used to measure the photoionization efficiency curves of 1,3-diethoxybenzene in electrostatic fields.From the linear fitting of the ionization energy values measured under different electric fields(Stark effect)to the square root of the field strengths,the precise ionization energy values of rotamer Ⅰ and rotamer Ⅲ are determined to be(62419±2)cm^(–1) and(63378±2)cm^(–1),respectively.Compared with the accuracies of the values measured by the usual pulsed electric field acceleration mechanism and the ZEKE spectroscopy,the accuracy is improved from about±10 and±5 to±2 cm^(–1),respectively.The physical mechanism,advantages and disadvantages of different methods are analyzed and discussed.The present research results show that the ionization energy measured in the electrostatic field is more accurate,the physical meaning of the measurement process is clear,and the threshold data are easy to collect.This is the first report on the precise ionization energy of 1,3-diethoxybenzene rotamers.