The difficulty in achieving high spectral resolution and accurate line shape in sum-frequency generation vibrational spectroscopy (SFG-VS) has restricted its use in applications requiring precise detection and quantitative analysis. Recently, the development of high-resolution broadband sum-frequency generation vibrational spectroscopy (HR-BB-SFG-VS) with sub-wavenumber resolution generated by synchronizing two independent amplifier lasers have opened new opportunities for probing an intrinsic SFG response. Here, we present a new flexible approach to achieve HR-BB-SFG-VS. In this system, two regeneration amplifiers shared the same oscillator laser as the seed, and a time-asymmetric visible pulse with a nearly Lorentzian line shape filtered by an etalon was used to overlap with a femtosecond broadband infrared pulse. This Lorentzian line shape of the visible pulse can greatly simplify the spectral fitting and analysis. We also demonstrated that the single-sided long visible pulse provided both high spectral resolution (1.4 cm−1) and effective suppression of the non-resonant background by detuning the time delay between visible and infrared pulses in SFG-VS measurements. With this new SFG setup, a pair of spectral splittings by 3.1 ± 0.7 and 3 ± 0.2 cm−1 for the symmetric and antisymmetric stretching of the CH3 group was resolved at the CH3CN/TiO2(110) surface, which are tentatively attributed to two different orientational methyl groups. These technological advancements can help broaden the applications of HR-BB-SFG-VS and provide solid ground for a better understanding of complex molecular structures and dynamics at interfaces.
Flexible high-resolution broadband sum-frequency generation vibrational spectroscopy for intrinsic spectral line widths
Note: This article is part of the Special Topic “Nonlinear Spectroscopy and Interfacial Structure and Dynamics” in J. Chem. Phys.
Ruidan Zhang, Xingxing Peng, Zhirun Jiao, Ting Luo, Chuanyao Zhou, Xueming Yang, Zefeng Ren; Flexible high-resolution broadband sum-frequency generation vibrational spectroscopy for intrinsic spectral line widths. J. Chem. Phys. 21 February 2019; 150 (7): 074702. https://doi.org/10.1063/1.5066580
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