Between A Phenol And Ether - Water Clusters Multiphoton Ionization Mass Spectrometry

Resonance enhanced multi-photon ionization (REMPI) technique improved with improving of lasers in late 1970s. This technique achieved dual selections (mass selection and spectroscopy selection) in ionization process and detection process. It has many merits: high sensitivity, high selectivity, high resolution etc. It's an effective technique in studying molecular energy levels, analyzing material composition, and environment pollutant detection etc. In the past few decades, along with the rapid development of the strong laser, harmonious laser and femto-second laser, the research of multi-photon process obtained rapid development. At present, the study of multi-photon ionization and dissociation process has already become one of the most important research areas of the atomic and molecular physics region.Cluster is a relative steady microcosmic or sub-microcosmic congeries which is composed of several or even thousands of atoms or molecules through chemical or physical combining force. In the past years, the study of clusters, especially hydrogen-bonded clusters, are attracting increasing attention. The hydrogen bond is a weak chemical interaction that plays an important role in many areas of chemistry. Many phenomena such as solvation, energy transfer and chemical reactions are influenced by the hydrogen bond, especially proton transfer reactions in hydrogen-bonded clusters.Phenols are methyloic. It can form hydrogen bond with H₂O or alcohols. Under normal circumstances, the polarization degree of Phenol hydroxyl is higher than alcohol, therefore, the hydrogen bonds formed with other molecules in phenols is stronger than corresponding alcohol. So, the study of phenols can help us understand the hydrogen bond. In addition, m-methylphenol is important derivant of benzene, so, more information of benzene can be obtained by the study of m-methylphenol.Diethyl ether as proton acceptor may form hydrogen bond with H₂O and alcohols molecules, so, we can know the mechanics how it interacts with other matter by the study of the diethyl ether-water mixed clusters. Besides, we may also learn more the proton transfer reactions mechanics in hydrogen-bonded clusters.This paper mainly consists of two parts. In the first part, using 355 nm laser as excitation source, m-methylphenol multiphoton ionization and dissociation (MPID) is studied, m-methylphenol TOF mass spectra of multiphoton ionization are obtained, There is no parent ion detected. By analysis, the main possible dissociation and ionization channel are attained. Using ab initio calculation to optimize the geometric structure of C₇H₈OH⁺ at B3LYP/6-311++G(d,p) level, the stable structure is obtained. By exploring thepotential energy surface of C₇H₈OH⁺, we conclude that the formation process of C₇H₈OH⁺ is a reaction process without potential barrier. In the second part, diethyl ether-water mixed clusters were studied by using multiphoton ionization technique and time-of-flight mass spectrometer, A series of protonated cluster ions were measured: (CH₃CH₂OCH₂CH₃)_nH⁺(n=1, 2,…, 6),(CH₃CH₂OCH₂CH₃)_nH₂OH⁺(n=1, 2, 3, 4)and (CH₃CH₂OCH₂CH₃)_n(H₂O)₂H⁺ (n=2, 3, 4). By researching the multiphoton ionization mass spectrum of diethyl ether-water mixed clusters , it is concluded that (CH₃CH₂OCH₂CH₃)₃H₂OH⁺ has magic structure. Using ab initio calculation to optimize the geometric structures of diethyl ether-water mixed clusters at B3LYP/6-31G(d) level, the stable structures are attained. By analyzing cluster's infrared vibrational spectrum, it is found that the main contribution to the strongest IR mode comes from the H stretch vibration of the hydrogen bond.This article includes the following aspects:1.The development and application of multiphoton ionization technique are expatiated; the introduction of cluster and hydrogen-bond cluster are provided; the methods of experiment and theoretical calculation about clusters are offered.2.Experimental equipments and experimental methods.3.Study on MPI-MS of the m-methylphenol. By analysis, the main possible dissociation and ionization channel are attained.4.Study on MS of the diethyl ether-water mixed clusters and theoretical calculation.