Kinoshita Erika, Sung Woongmo, Nihonyanagi Satoshi, Okuyama Hiroshi, Tahara Tahei
Molecular Spectroscopy Laboratory, RIKEN, 2-1 Hirosawa, Wako 351-0198, Japan.
Department of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.
J Phys Chem Lett. 2025 Jan 30;16(4):1088-1094. doi: 10.1021/acs.jpclett.4c03223. Epub 2025 Jan 22.
Elucidation of the vibrational relaxation process of interfacial water is indispensable for understanding energy dissipation at the aqueous interface. In this study, the vibrational relaxation dynamics of the hydrogen-bonded OH (HB OH) stretch vibration was investigated at the air/isotopically diluted water (HOD-DO) interface by time-resolved heterodyne-detected vibrational sum frequency generation (TR-HD-VSFG) spectroscopy. We observed the temporal change of the excited-state band ( = 1 → 2 transition), which enables a reliable determination of the time of interfacial water. The times obtained for the HB OH stretch with various pump frequencies are 0.14 ± 0.15 ps (3200 cm), 0.27 ± 0.05 ps (3300 cm), 0.34 ± 0.03 ps (3400 cm), and 0.63 ± 0.04 ps (3500 cm), indicating that is comparable with the value at the air/HO interface at the low-frequency side but is markedly longer at the high-frequency side. The observed frequency-dependent time can be rationalized in terms of the frequency mismatch between the HB OH stretch and the bending overtone in HOD-DO, supporting the conclusion that vibrational relaxation through the Fermi resonance with the bending overtone is the predominant mechanism of the vibrational relaxation of the HB OH stretch at the air/water interface.
阐明界面水的振动弛豫过程对于理解水相界面处的能量耗散至关重要。在本研究中，通过时间分辨外差检测振动和频产生（TR-HD-VSFG）光谱，研究了空气/同位素稀释水（HOD-DO）界面处氢键合的OH（HB OH）伸缩振动的振动弛豫动力学。我们观察到激发态谱带（= 1 → 2跃迁）的时间变化，这使得能够可靠地确定界面水的时间。不同泵浦频率下HB OH伸缩振动的时间分别为0.14 ± 0.15 ps（3200 cm）、0.27 ± 0.05 ps（3300 cm）、0.34 ± 0.03 ps（3400 cm）和0.63 ± 0.04 ps（3500 cm），表明在低频侧与空气/H₂O界面处的值相当，但在高频侧明显更长。观察到的频率相关时间可以根据HOD-DO中HB OH伸缩振动与弯曲泛频之间的频率失配来解释，这支持了通过与弯曲泛频的费米共振进行振动弛豫是空气/水界面处HB OH伸缩振动的主要振动弛豫机制这一结论。
