Resonant interaction between local vibrational modes and extended lattice phonons in AlSb

Using infrared spectroscopy we have observed Se-H stretch and wag local vibrational modes (LVM's) in AlSb. The frequencies of the wag mode harmonics are explained by perturbation theory. In addition, there is evidence of a resonant interaction between LVM's and multi-phonon modes. This interaction leads to a splitting of the Se-H stretch mode into three peaks at 1606.3, 1608.6, and 1615.7 cm(-1) at liquid-helium temperatures. As the temperature or pressure is increased, the stretch mode and multi-phonon modes show anti-crossing behavior.