Reliable estimation of Raman shifts for peaks of L-cystine (NMIJ CRM 6025-a) in the low-frequency region.

Raman scattered light is generated by the interaction of irradiated light with molecular vibrations, and it provides molecular information. Although Raman shifts of peaks in the low-frequency region (< 200 cm) provide useful information related to molecular structures, there are no reliable materials available for calibrating Raman spectrometers in this region. In this study, we chose high-purity L-cystine (NMIJ CRM 6025-a) and used it to reliably evaluate Raman shifts of peaks with uncertainty by a combination of HeNe laser and Ne emission lines. To evaluate their uncertainty, we considered the uncertainty originating from wavenumbers of Ne emission lines and HeNe laser, evaluation of wavenumber for peak-tops and changes in temperature. The obtained Raman shifts of eight peaks from 9 to 160 cm and their uncertainty were 0.3 cm or 0.4 cm and these values were validated with the results using a 532 nm laser.