Ultrafast vibrational relaxation of diatomic chalcogen hydrides in alkali halides

Abstract

Articles you may be interested inRotational spectrum of SO3 and theoretical evidence for the formation of sixfold rotational energy-level clusters in its vibrational ground state Terahertz spectroscopy and solid-state density functional theory calculation of anthracene: Effect of dispersion force on the vibrational modes Ab initio potential energy and dipole moment surfaces, infrared spectra, and vibrational predissociation dynamics of the 35 Cl − H 2 / D 2 complexesThe energy relaxation times of the fundamental stretching modes in the electronic ground state of OH Ϫ , OD Ϫ , SH Ϫ , and TeH Ϫ in a variety of alkali halides are measured by incoherent laser saturation and found to vary from 0.3 to 3 ns at 1.7 K. These vibrational lifetimes are between 4 and 8 orders of magnitude smaller than those of other heteronuclear diatomics diluted in crystals, including the ionic systems of CN Ϫ in salts and the neutral deuterides, DCl and ND, and oxides, CO and NO, in rare-gas matrices. Unlike these other systems, the chalcogen-hydride-doped alkali halides have a librational mode at frequencies well above the top of the host phonon band. This makes the librational decay channel a lower order process than relaxation into phonons. An energy gap law can be fit to the data, in which the relaxation times vary exponentially with the number of accepting reorientational modes. This model can explain the fact that OH Ϫ and OD Ϫ in KCl have nearly the same lifetimes, since the vibrational and librational frequencies both have the same isotope shift. Furthermore, previous persistent spectral hole burning measurements of SH Ϫ in mixed crystals are consistent with a picture in which the defects reorient during vibrational de-excitation. It is found that the reorientational decay rates are much faster than the equal-decay-order relaxation of CN Ϫ into translational modes in the silver and sodium halides. This could be explained by a factor of ϳ3 enhancement in the vibrational coupling constant to reorientations as compared to translations, but the relative strengths of the appropriate sidebands do not appear to support such an enhancement. The relaxation times of the diatomic hydrides are also found to be much smaller in ionic than in van der Waals hosts, even for equal order reorientational relaxation, suggesting that Coulombic forces significantly increase the V -R coupling strength.

Transformations in Crystalline Ammonium Nickel Tutton Salt Induced by Infrared Hole Burning

“…16,17 Our investigation shows at least one possible mechanism for these anomalies: there are multiple spectral diffusion/ reaction mechanisms that occur on the time scale of the laser irradiation.…”

Aligning and orienting molecules trapped in octahedral crystal fields

“…[43,44], where also the interaction with the matrix was estimated. Other work giving explicit values of κ can be found from spectroscopy [32,39,[51][52][53] and modelling [35,49,54] of librational states. Experimental verification of the schemes as proposed in the present work poses a significant challenge.…”

“…This is often realized for impurities which are small enough to fit in a mono-substitutional lattice site such that their rotational motions are only moderately influenced by the surroundings. For instance, hydrogen halides or other small diatomic molecules in solid rare gases [30,31], in alkali halide crystals [32,33], or at interstitial sites of the fullerite [34,35] come into question.…”

Intense-Field Alignment of Molecules Confined in Octahedral Fields

“…We restrict ourselves to the case 123003-2 of 50 where the potential wells are deep enough to support directional states while the energy spectrum is still sufficiently far from that of the librational limit, thus representing typical crystal fields [8] and matrix-isolation applications [12]. Without loss of generality, we study only the lowest four totally symmetric states (A 1g ) of the D 4h subgroup.…”

“…Such a situation is realized, e.g., for molecules embedded in solid rare gases [6], alkali halides [7,8], or fullerites [9,10]. The ranges of crystal field and laser strength parameters cover those relevant for small molecules in rare gas crystals [11,12] for which alignment experiments are underway.…”