Vibrational absorption of tunneling molecular defects in crystals. II. Tunneling molecules under applied stress (KCl:CN - )

摘要: The general considerations about the vibrational absorption of tunneling molecules, developed in Paper I this work, are applied and tested, using ${\mathrm{CN}}^{\ensuremath{-}}$ defects KCl. In previous work on system was reported to be strongly broadened by an unresolved splitting, show pure zero-moment changes under stress. model, however, predicts additionally characteristic anisotropic spectral shape field or stress for any absorption, orientational tunneling. A thorough experimental reinvestigation at low temperatures yields results which agree with predictions from model. For concentration, first- second-harmonic (at 5 2.5 \ensuremath{\mu}m) consists a resolved double structure, caused reorientational molecule crystal (tunneling splitting $\ensuremath{\Delta}=1.2$ ${\mathrm{cm}}^{\ensuremath{-}1}$). application uniaxial different symmetry is found produce two basic effects: Second-moment (due quantum-mechanical mixing states stress), classical elastic dipole alignment). observed pronounced anisotropy these effects yield both independently (cigar-shaped) 111g These disagree (pancake-shaped) 100g dipole, derived earlier elastooptical has been basis so far generally accepted defect Consequences change interpretation several investigations KCl:C${\mathrm{N}}^{\ensuremath{-}}$ will discussed.