Mr. Pardanaud, the answer of your question is yes. And these crystals are very distinguished especially within THz-region.

depensing of the laser exitation and the temperature you can observed:

CsI (Ag1+Eg+T2g) ca 120 cm-1. It has also LO and To below 100 cm-2, but it is out of the range of your interest.

KBr: A1g+Eg+2Tg at ca. 150 cm-1, A1g+2Eg+2T2g ca. 130 cm-1, A1g+Eg ca. 220 cm-1, and T2g ca. 210 cm-1.

NaCl: 2T2g 230 cm-1, and A1g+2Eg+2T2g ca.350 cm-1

These are data with 1064, 515 and 365 nm lasers excitation energy. With the 365 nm is possible in NaCl to observed as well a frequency at 250 cm-1 (25oC).

Suitable refs are:

1. Opt. Commun 19 (1976) 108

2. J. App. Phy. 47 (1976) 2467

3. Phy. Stat. Solidi. 50 (1972) 155

4. Phys. rev. B. 10 (1974) 4358.

It should be better if you perform measurements, polisheing peaces of KBr, CsI and NaCl pellets from IR cuvettes. For example 0.5 cm3 at given fixed experimental conditions (lex, T).

Mr. Krylov, Nakamoto's books are not suitable in this case. really they contained fundamental basis of the molecular vibrations, the efforts are mainly on organic compounds and inorganic salts of transition metal ions, edue to the main interest on coordination metal-organic chemistry. For Mr. Pardanaud shall be more useful to recognize with comprehensive studies on multiphonon processes in the crystals. Even above mentioned are not representative part, only few examples.

This pure crystals have no Raman spectra. Why? Read, for example, this book: Kazuo Nakamoto. Infrared and Raman Spectra of Inorganic and Coordination Compounds, Part A, Theory and Applications in Inorganic Chemistry, 6th Edition ( http://eu.wiley.com/WileyCDA/WileyTitle/productCd-0471743399.html )

Thanks for the book.

I know that there is an optical phonon for NaCl for example. It is a good new for Raman men as we probe the center of the Brillouin zone. May be the symmetry and the way we are looking on it with a polarized laser say "there is no Raman signal", however, I think it also depends on the defect concentration. For defectuous samples, they may be some local modes which may become Raman active. Any reference on that ? Thanks in advance. cp

Hi Cedric

There is a journal fully based on raman spectroscopy

"Journal of Raman Spectroscopy"

you will get your answer in this journal.

Dear Cédric,

It is possible violation of the selection rules in crystal with defects. But violation strongly depends on type or/and amount of defects. Try use Google.

For you may be interesting:

C. Raptis. Evidence of temperature-defect-induced first-order Raman scattering in pure NaCl crystals // Phys. Rev. B 33, 1350–1352 (1986) ( http://prb.aps.org/abstract/PRB/v33/i2/p1350_1 )

Mr. Pardanaud, the answer of your question is yes. And these crystals are very distinguished especially within THz-region.

depensing of the laser exitation and the temperature you can observed:

CsI (Ag1+Eg+T2g) ca 120 cm-1. It has also LO and To below 100 cm-2, but it is out of the range of your interest.

KBr: A1g+Eg+2Tg at ca. 150 cm-1, A1g+2Eg+2T2g ca. 130 cm-1, A1g+Eg ca. 220 cm-1, and T2g ca. 210 cm-1.

NaCl: 2T2g 230 cm-1, and A1g+2Eg+2T2g ca.350 cm-1

These are data with 1064, 515 and 365 nm lasers excitation energy. With the 365 nm is possible in NaCl to observed as well a frequency at 250 cm-1 (25oC).

Suitable refs are:

1. Opt. Commun 19 (1976) 108

2. J. App. Phy. 47 (1976) 2467

3. Phy. Stat. Solidi. 50 (1972) 155

4. Phys. rev. B. 10 (1974) 4358.

It should be better if you perform measurements, polisheing peaces of KBr, CsI and NaCl pellets from IR cuvettes. For example 0.5 cm3 at given fixed experimental conditions (lex, T).

Mr. Krylov, Nakamoto's books are not suitable in this case. really they contained fundamental basis of the molecular vibrations, the efforts are mainly on organic compounds and inorganic salts of transition metal ions, edue to the main interest on coordination metal-organic chemistry. For Mr. Pardanaud shall be more useful to recognize with comprehensive studies on multiphonon processes in the crystals. Even above mentioned are not representative part, only few examples.

Thank you very much !