Studies on gap modes and localized modes due to BO2-, N3-, OCN-, SCN-, and SeCN- centres in KI

Abstract

We have studied gap modes and localized modes above the optical band due to a series of three-atomic linear centres (BO-2, N-3, OCN -, SCN-, SeCN-) in KI by Raman scattering and by vibrational sideband absorption in the middle infra-red We compare our results with previous investigations of far infra-red absorption. A set of three gap modes (A2u ⊕ Eu ⊕ Eg or A u ⊕ 2 E) is established for each centre by experiment — according to group theory. The frequency behaviour within the series of centres is discussed by a linear model. This model explains also the appearance of up to four transverse (E) localized modes which are ascertained by experiment The comparison of sideband absorption and Raman scattering spectra shows that both phenomena obey the same selection and intensity rules. These rules can be deduced theoretically by the Wigner-Eckart theorem and are physically interpreted