INFRARED-SPECTROSCOPY OF THE STRETCHING MODES OF SEH- AND TEH- IN KCLAND KBR

The fundamental stretching modes near 4.5 mu m of SeH- and TeH- doped in KCI and KBr are measured at high resolution at 1.7 K. For the KCl-d oped samples, prepared by adding elemental Se (Te) to the melt and gro wing under H-2, the concentrations of atomic Se (Te) are determined by neutron activation analysis. An IR/Raman/UV spectroscopic survey of i mpurities in these crystals indicates that Se(Te) is present mainly in the form of SeH-(TeH-). Thus, ratioing the vibrational absorption str engths to the atomic concentrations gives the integrated cross-section s of SeH-(TeH-), equivalent to an effective charge q of similar to 0. 14e and a radiative lifetime of similar to 30 ms. This value of q is much smaller than theoretical predictions for the free ions, implying a matrix-induced screening of the dipole moment. The lowest-order mech anical anharmonic correction to the vibrational frequencies is found t o be similar to 2% by measuring the first overtones and is used to fit the isotopic shifts in the spectral peaks. These peaks are homogeneou sly broadened at 1.7 K; if lifetime limited, this implies a vibrationa l relaxation of the order of 100 ps, nine orders of magnitude faster t han the radiative lifetime.