2026-04-22 九州大学
同位体置換によるラマンスペクトル変化の模式図。酸素同位体の増加に伴い、ピークは低波数側へシフトし（質量効果）、置換サイトの違いによりピーク分裂が生じ、対称性の低下によりピークの広がりが生じる。
＜関連情報＞
- https://www.kyushu-u.ac.jp/ja/researches/view/1459
- https://www.kyushu-u.ac.jp/f/65761/26_0422_02.pdf
- https://pubs.acs.org/doi/10.1021/acs.jpcc.5c08487
フォルステライト（Mg2SiO4）のラマンスペクトルに対する酸素同位体効果の計算解析 Computational Analysis of Oxygen Isotope Effects on the Raman Spectra of Forsterite (Mg2SiO4)
Masashi Arakawa
The Journal of Physical Chemistry C Published: April 21, 2026
DOI:https://doi.org/10.1021/acs.jpcc.5c08487
Abstract
The dependence of Raman spectra of forsterite (Mg2SiO4) on oxygen isotopic ratios was systematically investigated using density functional theory (DFT) calculations with the CRYSTAL17 code. Si–O stretching vibrational frequencies and Raman intensities were computed for a series of isotopic compositions (α = 17O/16O, 18O/16O) over the α = 0.0159–0.143 range, employing unit-cell and, for lower α values, supercell models, as well as for the end-member structures at α = 0.000 and 1.000. Partial isotopic substitution breaks the lattice symmetry, activating originally Raman-inactive modes, while site-dependent substitution induces band splitting. The simulated spectra quantitatively reproduce the experimentally observed red shifts with increasing heavy-oxygen fractions and explain the broadening of the major peaks near 810 and 960 cm–1 through a combination of symmetry reduction and site-specific effects. These results provide microscopic insight into the influence of isotopic substitution on the Raman response of forsterite and establish a theoretical foundation for future micro-Raman studies aimed at precise oxygen isotopic ratio determination.
