物理化学学报 >> 2010, Vol. 26 >> Issue (01): 94-98.doi: 10.3866/PKU.WHXB20100135

光化学与光谱 上一篇    下一篇

N2O分子C1∏态的吸收光谱及解离动力学

甄承, 胡亚华, 刘世林, 周晓国   

  1. 合肥微尺度物质科学国家实验室(筹), 中国科学技术大学化学物理系, 合肥 230026
  • 收稿日期:2009-09-17 修回日期:2009-10-30 发布日期:2009-12-29
  • 通讯作者: 周晓国 E-mail:xzhou@ustc.edu.cn

Absorption Spectrumand Dissociation Dynamics of the C1∏ State of N2O

ZHEN Cheng, HU Ya-Hua, LIU Shi-Lin, ZHOU Xiao-Guo   

  1. Hefei National Laboratory for Physical Sciences at the Microscale, Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, P. R. China
  • Received:2009-09-17 Revised:2009-10-30 Published:2009-12-29
  • Contact: ZHOU Xiao-Guo E-mail:xzhou@ustc.edu.cn

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摘要：

通过四波混频差频的方法产生高分辨的真空紫外激光, 用以测量143.6至146.9 nm范围内的射流冷却N2O分子吸收光谱, 对应于C1∏←X1∑+的吸收跃迁. 谱图显示出三个分立的振动谱峰叠加在宽吸收背景上, 谱峰间隔分别是521和482 cm-1. 前人的高精度量子化学计算表明C1∏态在N—O键长方向表现为无势垒的排斥态, 而在N—N键伸缩及N2O弯曲振动方向则表现为束缚态, 因此观测到的振动谱峰被归属为激发态的Feshbach共振. 通过反Fourier变换可以得到Feshbach共振对应的非稳定周期轨道的特征周期为61 fs, 相应的振动频率为546 cm-1. 鉴于这一频率与弯曲振动频率非常接近, 非稳定周期轨道被认为是由C1∏态的弯曲振动与解离运动相互作用而形成的, N—N伸缩振动没有参与形成非稳定周期轨道. 由此, N2O分子C1∏态光激发-解离过程得以清晰地阐述.

关键词: 吸收光谱, 一氧化二氮, 真空紫外光, 解离

Abstract:

The absorption spectrum of the N2O molecule in the wavelength range of 143.6-146.9 nm was measured under the jet-cooled condition by using the high resolution vacuum ultraviolet radiation, which was generated by resonance-enhanced difference-frequency mixing, corresponding to the C1∏←X1∑+ transition. Three vibrational bands were observed with frequency intervals of 521 and 482 cm -1, and they were superimposed on a wide absorption background. Previous high-level quantum chemical calculations indicate that the C1∏ state of N2O is dissociative along the N—O elongation, while it is bound along the N—N bond stretching or N2O bending. Therefore, the observed vibrational progression is a Feshbach resonance of the dissociative transition state. From an anti-Fourier transformation analysis, the recurrence period of the unstable periodic orbit of the Feshbach resonance was found to be 61 fs and the corresponding vibrational frequency was 546 cm-1. Since this vibrational frequency is close to the frequency of the bending motion, the unstable periodic orbit is mostly composed of the bending motion of the C1∏ state coupled with dissociation. The N—N stretching vibration does not participate in its formation. Therefore, we describe the excitation-dissociation dynamics of the C1∏state of N2O clearly.

Key words: Absorption spectrum, N2O, Vacuumultraviolet, Dissociation