运用二阶非线性光谱技术（和频与倍频）研究表/界面结构以及对在表/界面发生的物理化学反应的机理和动力学的研究。和频（sum frequency generation）的产生是一种二阶非线性光学过程，在偶极近似下，由跃迁选择定则的要求，该过程的发生只能存在于不对称的环境中，所以对于中心反演对称的体系（比如体相水），不能贡献和频信号。然而，由于表面其对称性本征的破缺，因此和频光谱具有表面/界面灵敏性。通常，我们用两束脉冲激光（ω1，ω2）同时照射到样品表面，使两束激光时间空间上重合，测量其和频（ω3=ω1+ω2）信号。其中一束入射光可以与表面分子的振动频率发生共振，因此调节入射光频率得到的和频光谱承载着表面分子的信息。通过分析和频光谱我们可以获得表面相关的分子极性取向、分子构象、平均倾角等。结合飞秒脉冲激光，时间分辨的和频光谱可以帮助我们理解表面物理化学反应的动力学过程。

1. Shumei Sun, Chuanshan Tian*, and Y. Ron Shen*, Surface sum-frequency vibrational spectroscopy of nonpolar media, Proc. Natl. Acad. Sci. U.S.A., 2015, 112, 5883.

2. Shumei Sun, Rongda Liang, Xiaofan Xu, Heyuan Zhu, Y. Ron Shen*, and Chuanshan Tian*, Phase reference in phase-sensitive sum-frequency vibrational spectroscopy, J. Chem. Phys., 2016, 144, 244711.

3. Shumei Sun, Rongda Liang, Xiaofan Xu, Heyuan Zhu, Y. Ron Shen*, and Chuanshan Tian*, Respond to "Comment on ‘Phase reference in phase-sensitive sum-frequency vibrational spectroscopy’", J. Chem. Phys., 2016, 145, 167102.

4. Shumei Sun^#, Fujie Tang^#, Sho Imoto, Daniel R. Moberg, Tatsuhiko Ohto, Francesco Paesani, Mischa Bonn*, Ellen H. G. Backus*, and Yuki Nagata*, The orientational distribution of free O-H groups of interfacial water is exponential, Phys. Rev. Lett., 2018, 121, 246101.

5. Shumei Sun, Pactrick J. Bisson, Mischa Bonn, Mary J. Shultz and Ellen H. G. Backus*, Phase-sensitive sum frequency generation measurements using a femtosecond nonlinear interferometer, J. Phys. Chem. C, 2019, 123, 7266.

6. Shumei Sun^#, Fujie Tang^#, Sho Imoto, Daniel R. Moberg, Tatsuhiko Ohto, Francesco Paesani, Mischa Bonn*, Ellen H. G. Backus*, and Yuki Nagata*, Response to "Comment on orientational distribution of free O-H groups of interfacial water is exponential", Phys. Rev. Lett., 2019, 123, 099602.

7. Takakazu Seki^#, Shumei Sun^#, Kai Zhong, Chun-Chieh Yu, Kevin Machel, Lisa B. Dreier, Ellen H. G. Backus, Mischa Bonn and Yuki Nagata*, Unveiling heterogeneity of interfacial water through the water bending mode, J. Phys. Chem. Lett., 2019, 10, 6936.

8. Rongda Liang^#, Huijie Xu^#, Yuneng Shen, Shumei Sun, Jiyu Xu, Sheng Meng, Y. Ron Shen* and Chuanshan Tian*, Nucleation and dissociation of Methane Clathrate Embryo at the Gas-water interface, Proc. Natl. Acad. Sci. U.S.A., 2019, 116, 23410.

9. Shumei Sun^#, Jan Schaefer^# Ellen H. G. Backus* and Mischa Bonn*, How surface-specific is 2nd-order non-linear spectroscopy, J. Chem. Phys., 2019, 151, 230901.

10. Sudipta Das, Sho Imoto, Shumei Sun, Yuki Nagata, Ellen H. G. Backus* and Mischa Bonn*, Nature of excess hydrated proton at the water-air interface. J. Am. Chem. Soc. 2020, 14, 945-952.

11. Fujie Tang, Tatsuhiko Ohto, Shumei Sun, Jérémy R. Rouxel, Sho Imoto, Ellen H. G. Backus, Shaul Mukamel, Mischa Bonn, and Yuki Nagata*, Molecular structure and modeling of water−air and Ice−air interfaces monitored by sum-frequency generation. Chem. Rev. 2020, 120, 3633-3667.

12. Takakazu Seki, Chun-Chieh Yu, Xiaoqing Yu, Tatsuhiko Ohto, Shumei Sun, Meister Konrad, Ellen H. G. Backus, Mischa Bonn, Yuki Nagata*, Decoding the molecular water structure at complex interfaces through surface-specific spectroscopy of the water bending mode.  Phys. Chem. Chem. Phys. 2020, 22, 10934-10940.

13. Chunyan Ma, Shumei Sun, Hao Lu, Zhengping Hao, Chenggong Yang, Bin Wang, Cheng Chen, Maoyong Song*,Remarkable MnO2 structure-dependent H2O promoting effect in HCHO oxidation at room temperature. J. Hazard. Mater. 2021, 414, 125524.

14. Guangliu Ran, Liang Zhou, Hao Wu, Haijun Fan, Shumei Sun*, Xiaozhang Zhu*, Wenkai Zhang*, Ultrafast dynamics investigationon efficient NDT-based small molecule heterojunctions. Acta Photonica Sinica 2021, 50 (8).

15. Takakazu Seki, Chun-Chieh Yu, Kuo-Yang Chiang, Junjun Tan, Shumei Sun, Shuji Ye, Mischa Bonn, Yuki Nagata*, Distangling sum-frequency generation spectra of the water bending mode at charged aqueous interfaces. J. Phys. Chem. B, 2021, 125, 7060-7067.

16. Xiaoqing Yu, Takakazu Seki, Chun-Chieh Yu, Kai Zhong, Shumei Sun, Masanari Okuno, Ellen H. G. Backus Johannes Hunger, Mischa Bonn*, Yuki Nagata*, Interfacial water structure of binary liquid mixtures reflects nonideal behavior. J. Phys. Chem. B 2021, 125 (37), 10639-10646.

17. Chun-Chieh Yu, Sho Imoto, Takakazu Seki, Kuo-Yang Chiang, Shumei Sun, Mischa Bonn*, Yuki Nagata*, Accurate molecular orientation at interfaces determined bymultimode polarization-dependent heterodyne-detected sum-frequency generationspectroscopy via multidimensional orientational distribution function. J. Chem. Phys. 2022, 156 (9), 094703.

18. Hao Lu*, Luca Belluci, Shumei Sun, Daizong Qi, Marta Rosa, Rüdiger Berger, Stefano Corni, Mischa Bonn*, Acidic pH promotes refolding and microscopic assembly of Amyloid β (16-22) peptides at the air-water interface. J. Phys. Chem. Lett. 2022, 13, 6674-6679.

19. Chun-Chieh Yu, Takakazu Seki, Kuo-Yang Chiang, Fujie Tang, Shumei Sun, Mischa Bonn*, Yuki Nagata*, Polarization-dependent heterodyne-detected sum-frequency generation spectroscopy as a tool to explore surface molecular orientation and Ångström-scale depth profiling. J. Phys. Chem. B 2022, 126, 33, 6113-6124.

20. Liang Zhou, Guangliu Ran, Yahui Liu, Zhishan Bo*, Shumei Sun*, Wenkai Zhang*, Thermal annealing effect on non-fused ring acceptor based bulk heterojunction investigated by transient absorption spectroscopy. J. Photoch. Photobio. 2022, 11, 100129