| This dissertation mainly presents the experimental studies on the photofragment excitation (PHOFEX) spectrum and photodissociation dynamics of the A2A1 state of H2S+ ions. Additionally, around this work an approach to obtain the photofragment translational energy distribution from time-of-flight (TOF) profile, an investigation on space-charge effect in the TOF mass spectrometer and the laser-induced fluorescence (LIF) from A2Î 1/2,3/2 (v=0, 1) state of CO+ are also developed.PHOFEX spectrum and photodissociation dynamics of H2S+ (A2A1)(1). Pure parent ions, H2S+ A2A1(000), were prepared by (2+1) multiphoton ionization of H2S molecules at 302.50nm. The photofragment S+ excitation spectrum were recorded by scanning another laser in the wavelength range of 317-420nm. The PHOFEX spectrum were assigned as H2S+ A2A1(v1v2v3)â†X2B1(000) transitions, which were observed for the first time and rotational analysis of the (1,7,0) K=2, (0,9,0) K=3, (0,10,0) K=2 and (0,11,0) K=0 band were presented. The spectral constants of the A2A1 state were obtained based on the assignment.(2). The appearance of the S+ fragment ions has been measured to lie at 23840±1cm-1 and at this position the S+ TOF profile has been observed to be asymmetric, which caused by the long lifetime of the excitation state. The lifetime has been obtained to be about 0.75μs by simulated TOF profile using the deduced expression. This asymmetric phenomenon perhaps results from the tunnel effect at the excitation energy under the dissociation potential barrier, which can be estimated to be about 24580±130cm-1. Above the dissociation potential barrier, the lifetime at different photolysis energies were estimated by the rotational line width and it was found the lifetime has little change as the excitation energy increased.(3). The total released translational energies ET and anisotropy parameterβat different photolysis energies have been obtained by fitted the S+ TOF profile. It was found that ET increases gradually with the increase of photolysis energy and the dissociation energy D0(S+-H2) was estimated to be about 23494cm-1 by fitted linear. In addition, when the photolysis energy is above 30760cm-1(correspond to the (0,13,0)K=1 band), the vibrational excitation v=1 of the H2 fragment molecules were observed.(4). It was observed that there are one or two rotational lines in the progression of (0,v2,0) K=1(v2=8-13) band, which not only the width of these lines is wider than others but also the corresponding S+ fragment TOF are two peaks (the photolysis laser polarization parallel to the TOF-MS axis).(5). The main dissociation channels in the photolysis energy range are suggested as S+(4Su)+H2(1∑g+) and SH+(3∑-)+H(2Sg), but only S+ fragment was observed. Based on the experimental results the dissociation mechanism of the channel S+ was proposed: a. around the barriers to linearity, the A2A1 state couples to the 4A2 state through the spin-orbit interaction, or to the X2B1 state through electron-vibration interaction (Renner-Teller effect) and X2B1 state then couples to the 4A2 state through the spin-orbit interaction leading to the S+(4Su)+H2(1∑g+) products; b. far from the barriers to linearity, the A2A1 state couples to the 4A2 state through the spin-orbit interaction leading to the S+(4Su)+H2(1Sg+) products.An approach to obtain the photofragment translational energy distribution from time-of-flight profileAt the magic angle the TOF-MS profile depends only on the translational energy distribution of photofragment, and is independent of the angle distribution of recoil momentum, therefore, the translational energy distribution is usually determined by fitting the measured TOF-MS profile. Different from the above procedure, we take another approach in the present work.. According to this method, by measuring three widths at half maximum (t1/2), one-fourth maximum (t1/4) and three-fourth maximum (t3/4) of the TOF-MS profile, the averaged translational energy, the width of translational energy distribution, as well as the width of instrumental function can be determined from numeric tables or mathematical expressions. In this method, both the translational energy distribution and the instrumental function are described by Gaussian functions.An Investigation on Space-charge Effect in the Time-of-flight Mass SpectrometerIn the multi-photon ionization experiment, we observed that the parent ion peak of time-of-flight (TOF) becomes broader with the laser power increasing. Briefly, this phenomenon is caused by the space-charge effect of ions. A qualitative theoretical model, that the ion cloud created by the laser has a spherical form and the initial charge distribution is Gaussian, is used to evaluate the full width at half maximum (FWHM), which depends on the laser intensity, the pressure of the sample gas, the extraction electric field, the ionic mass, and the focal length of the lens employed. The proposed model agrees well with our experimental data.Laser induced fluorescence excitation spectrum of CO+(A2Î 1/2,3/2-X2∑+)The Laser induced fluorescence (LIF) excitation spectrum of CO+ (A2Î 1/2,3/2-X2∑+)has been recorded under supersonic jet-cooled conditions. The CO+ X2∑+ ions were prepared by 2+1 REMPI of neutral CO molecules at 230nm and the LIF spectra of CO+ (A2Î 1/2,3/2-X2∑+) ions were measured by scanning another laser in the range of 453-459nm and 487-493nm, which belong to 1-0 and 0-0 band respectively. Although the REMPI-LIF is a good method to investigate the ion spectroscopy and structure, it is only applicable to the molecule with great ionization cross section.
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