Hyper-Raman spectroscopy
Unique information is brought from vibrational spectroscopy. IR and Raman spectroscopy has been employed for the measurement of molecular vibration and for the structural chemistry. Hyper-Raman (HR) spectroscopy is known as the third method of the vibrational spectroscopy. Due to difference in the selection rule, the spectral pattern of the HR spectrum is different from the IR and Raman spectra. That is, the HR spectroscopy provides a new tool for the structural analysis.

The excitation beam was 532 nm emission line of ps-pulse Nd:YAG laser (Taliskar 355-4 Ultra, Coherent)(Figure (a)). The scattered signal at 90˚ was collected (Figure (b)). Owing to high repetition rate (200 kHz) of high-power (300 mW) short (15 ps) pulse, the HR spectrum was recorded with high S/N ratio[1].



Application to Biomolecules: Bovine Serum Albumin [2]
We have applied the HR spectroscopy to bovine serum albumin (BSA) as a soluble globular protein. The intensity pattern of HR spectrum resembled to that of the UV resonance Raman spectrum, and the detected HR bands were mostly assignable to the vibrations of Trp and Tyr, of which the intensity was enhanced with the resonance effect to 266 nm (doubled energy of 532-nm light). Some IR-active bands were also detected.



Application to Biomolecules: twenty amino acids [3]
It is of fundamental importance to understand the spectral features of the 20 amino acids, since they are the building block of the protein. The complete data set of the HR spectrum of the amino acids serves as a clue to analyze the HR bands of proteins, thereby assisting the discussion of the structure and structural changes thereof. We have applied the HR spectroscopy to twenty amino acids. By analogy to the Raman spectrum, the assignments were given for the observed HR bands.


[1] V.Korepanov, C.C.Yu, H.Hamaguchi, J. Raman Spectrosc. 2018, 49, 1742-1746.
[2] C.I.Wen, H.Hiramatsu, J. Raman Spectrosc. 2020, 51, 274-278.
[3] C.I.Wen, C.N.Yu, N.Thirumalaivasan, H.Hiramatsu, J. Raman Spectrosc. 2021, 52, 641-654.