激光诱导荧光光谱研究二氧化硫和硫化氢离子低电子态结构

The spectroscopic studies of molecular ions can provide important information for the physical chemistry and relative sciences. The development of the new techniques, such as high-resolution laser, supersonic molecule beam and laser induced fluorescence (LIF), had made it possible to study those unstable molecules, including free radicals and molecular ions..Sulpher dioxide (SO2), hydrogen sulfide (H2S) and the corresponding cations play important roles in the environment field, atmospheric chemistry and industry of semiconductor dry etching process. So far, the knowledge about the electronic structures and dissociation dynamics of SO2+ and H2S+ is still too limited, although several experimental methods have been used to study the low-energy electronic structures of SO2+ and H2S+, such as the photoelectron spectroscopy (PES), pulsed-field ionization-photoelectron spectroscopy (ZEKE/MATI), the photo predissociation spectroscopy, the photoion-fluorescence photon coincidence study, resonance-enhanced multiple-photon ionization (REMPI), and so on. However, for the SO2+, the existing high-resolution experimental result which was from the dissociation spectroscopy was limited be the dissociation channel and dynamics, moreover because of the difficulty from the strong emission (SO and/or SO+) background, there is no LIF study has been reported up now. For the H2S+, the ground and first excited states， which are from Renner-Teller pair, have dramatic change in bent angle, leading to the complex sepctroscopic structures especially above the bent-to-linear barrier. Therefore, the high-resolution LIF spectroscopy is needed to make more detailed study. .The aim of this work is to investigate the electronic structures of SO2+ and H2S+ by accurately measuring the vibrational and rotational energy levels in the low-energy electronic states with LIF spectroscopy, where the SYNC-LIF technology newly invented is the most important tool to identify the desired ionic fluorescence from noisy emission background. The concerted experimental and quantum chemistry computational study will allow a complete understanding of the equilibrium geometries and electronic structures in these systems.

二氧化硫SO2和硫化氢H2S分子及其对应离子，在大气化学、环境科学、工业半导体加工等领域发挥着重要作用。然而直到目前对于SO2+和H2S+的谱学实验研究十分有限，严重的限制了对其电子态结构和解离动力学的认识。本申请利用新建成的高灵敏、高分辨的激光诱导荧光光谱（LIF）实验装置，研究SO2+和H2S+分子离子的电子基态和低能量激发态结构。实验精确测量SO2+和H2S+的振动/转动分辨的激光激发光谱和发射光谱，通过光谱分析，确定电子态的对称性，获得离子在不同电子态的转动常数、振动频率、非谐性常数等光谱常数，键长、键角等几何构型，电子态中存在的电子自旋轨道耦合、Renner-Teller效应、费米共振等各种相互作用大小及类型等，给出两离子电子态势能面特征的信息，结合并对比量子化学计算结果，进一步加深对SO2+和H2S+低电子态结构的理解。

项目拟计划利用激光光谱对H2S+和SO2+的低电子态结构进行研究，对其中存在的电子-振动态耦合等奇特现象进行更全面的认识。依托基金支持，我们完成了激光光谱实验平台的搭建、在该平台上进行了原子发射光谱等离子体诊断、放电产物飞行时间质谱分析、S2自由基激光光谱等实验。实现了自由基的产生、诊断、质谱分析、光谱测量等一套完整的实验过程和量子化学计算研究。实验中，质谱没有观测到H2S+，而得到大量的H3S+离子和对应团簇分子离子，我们通过量子化学计算对其进行了解释；实验观测到SO2+离子质谱，但是没有观测到其光谱，可能原因是SO2分子在相同激光波长区域内有大量的荧光信号，掩盖了离子的荧光信号。S2分子在环境科学和空间科学研究中有重要价值，其低电子激发态B3Sigmau和B''3Pi之间存在强烈的耦合，是研究电子态耦合效应的典型体系。我们得到了转动分辨的71支振动跃迁光谱，经过转动拟合得到精确的分子常数，为进一步研究3Sigma-3Pi电子态耦合效应提供了重要参考数据。