External, internal and semi-internal vibrations in molecular solids: spectroscopic criteria for identification
✍ Scribed by Paras N. Prasad; Raoul Kopelman
- Publisher
- Elsevier Science
- Year
- 1973
- Tongue
- English
- Weight
- 508 KB
- Volume
- 21
- Category
- Article
- ISSN
- 0009-2614
No coin nor oath required. For personal study only.
✦ Synopsis
A new method to identify the nature of vibrations in molecular crystals as external oi internal is proposed. The criterion is that in isotopic mi..ed crystals of protonaled and ccrresponding perdeuterated compounds, the external motions (phonons) are in the amal,grnation limit, while the internal modes, and the "semi-internal" methyl torsions, are usually in the separated band limit. This criterion is slppor:ed by experimental isotopjc rnhed crystal studies of many molecular crystals. Previous criteria, like temperature and isotope shifts, are shown to be less reliable.
Anthracenc and biphcnylRaman spectra, as ~011 as literature data, are used as illustrations.