Dimethylamine And Propylamine Multiphoton Ionization Mass Spectrometry Studies

Since the emergence of the laser, the laser technology has been applied widely, which has also brought up a large number of efficient experimental methods concerning with laser. Among them one kind is multiphoton ionization that appeared during 1970s and blossomed during 1980s. Multiphoton ionization means that molecules or atoms absorb one or several photons to be triggered into a medium quantum state and then further absorb one or several photons to cause ionization. Especially under the condition of resonance, the ionizing efficiency for the molecules or atoms can be further increased, which can also improve the detection efficiency of the experiments greatly. The REMPI 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.The amine substance which, as an important living matter, exists widely in the tissues, organs and foods has served as a critical role for the physiological action. Due to its low ionizing potential, it only needs several photons to achieve ionization in the visible region. Furthermore, the Electron Impact of Mass Spectrum and the vacuum ultraviolet single-photon ionization have made a great deal of research on them and its results can be easily obtained. Therefore, the amine has been one substance that the multiphotons ionization is more interested to.The paper mainly consists of two large parts. In the first part, the dimethylamine was studied by using multiphoton ionization technique and time-of-flight mass spectrometers under the excitation of the 355 nm laser, we believes that it mainly undergoes the 2+1 REPMI process. The dimethylamine parent ion has gone through the a cleavage to produce CH₃N⁺H=CH₂ fragment which later dissociates to C₂H₄N⁺ fragment.The paper also obtains the result that the m/z42 fragment is CH₃N⁺≡CH by the ab initio calculations, and, meanwhile, make speculation of the possible sources of m/z28 fragment. One case is that the CH₃N⁺≡CH ion undergoes the further rearrangement that causes the loss of CH₂ radical ion. The other case is that the CH₂=N⁺H has lost one molecular hydrogen. In the second part, the multiphoton ionization and dissociation process of isopropylamine and n-Propylaminewere studied under the excitation of the 266nm laser by means of the laser mass spectrometry. What' more, the kinds of ion produced during the multiphoton ionization are much the same, but the ways to produce the ion are different. In the n-Propylamine, the parent ion produces the m/z 30 fragment through an apparent a cleavage. The m/z 30 fragment lose hydrogen to produce m/z28 fragment. The CH3CH2 neutral fragment further absorbs photons to produce the CH_x⁺ (x=0-3) and C₂H_x⁺(x=0,2,3) ions. There is no detection of parent ion during the multiphoton ionization mass spectrometry process. It mainly discusses the possible sources for the m/z(28,42,44,58)fragments and also obtains the result of the m/z42 fragment is CH₃C≡N⁺H which sources resembles like dimethylamine. In the isopropylamine mass spectra, the source of m/e28 is different from that of n-Propylamine. Furthermore, the regular cluster ion of both n-Propylamine and isopropylamine has been detected in the experiments.The contents of the paper are arranged as follows:1. The brief introductions, including the multiphoton ionization and TOF-MS, the important calaulations in the experience, the present studies of the subject.2. Experimental devices and experimental methods.3. The introduction of amines and theory of organic mass spectrometry.4. Study on MPI-MS of dimethylamine under the excitation of 355 nm laser5. Study on MPI-MS of n-Propylamine and isopropylamine under the excitation of 266 nm laser.