Structure-dependent vibrational lifetimes of hydrogen in silicon

The lifetimes of the Si-H vibrational stretch modes of the H(*)(2) ( 2062 cm(-1)) and HV.VH((110)) ( 2072.5 cm(-1)) defects in crystalline Si are measured directly by transient bleaching spectroscopy from 10 K to room temperature. The interstitial-type defect H(*)(2) has a lifetime of 4.2 ps at 10 K, whereas the lifetime of the vacancy-type complex HV.VH((110)) is 2 orders of magnitude longer, 295 ps. The temperature dependence of the lifetime of H(*)(2) is governed by TA phonons, while HV.VH((110)) is governed by LA phonons. This behavior is attributed to the distinctly different local structure of these defects and the accompanying local vibrational modes.     

Theoretical study of nonadiabatic interactions,radiative lifetimes and predissociation lifetimes of excited states of BH

Ab initio multireference configuration interaction calculations have been carried out on the lower-lying electronic states of BH and their nonadiabatic interactions. The ab initio data have been included in subsequent calculations involving solution of the complex eigenvalue Schrödinger equation to determine predissociation widths and lifetimes of vibrational-rotational levels of these states. Secondly, previously calculated ab initio data on the Rydberg states and their nonadiabatic interactions have been included in multi-state vibrational calculations on the 3p and 3d complexes in BH and BD. The results are in good agreement with the experimental analysis of the 3p and 3d spectra in BH and BD. Furthermore, interaction of the 3d states with the neighbouring 4s state is also found to be important.     

First-principles calculations of vibrational lifetimes and decay channels: hydrogen-related modes in Si

The vibrational lifetimes and decay channels of local vibrational modes are calculated from first principles at various temperatures. Our method can be used to predict the temperature dependence of the lifetime of any normal mode in any crystal. We focus here on the stretch modes of H2*, H+(BC), and VH x HV in Si. The frequencies are almost identical, but the lifetimes vary from 4 to 295 ps. The calculations correctly predict the lifetimes for T > 50 K and illustrate the critical importance of pseudolocal modes in the decay processes of high-frequency local vibrational modes.     

Nonlinear interaction of vibrational mode interactions in radiationless transitions

A method is proposed for calculating the transition probability in a two-level electron-vibration system, using a generating functional. Harmonic terms are used for the zeroth approximation. In the analysis of anharmonic terms the method makes it possible to transcend the limits of conventional perturbation theory with respect to the anharmonicity parameter. In the formulated cumulant expansion the method can be used to obtain a representation for the transition probability with allowance for convergence of the vibrational energy levels toward the dissociation limit.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 68–72, June 1981.     

D-meson lifetimes and decays

We discuss the theoretical implications of having the D⁺ lifetime be much greater than that of the D⁰. A consistent phenomenology of D-decay obtains if one assumes sextet dominance and strong color clustering.     

The influence of lateral interactions on the vibrational spectrum of adsorbed CO

Vibrational spectroscopy of adsorbed CO often reveals strong shifts of the CO stretch absorption band to higher frequencies as a function of increasing coverage. It is shown that such shifts are due essentially to dipole-dipole interactions. The extent of the experimentally observed effect can, however, only be reproduced when screening by the substrate is taken into account properly.     

Inclusive charmed-baryon decays and lifetimes

We have quantitatively reanalyzed the inclusive charmed-baryon decays. New ingredients are the Voloshin preasymptotic effects in semileptonic decays and the Cabibbo-subleading contributions to both semileptonic and nonleptonic decays. It has been found that the Cabbibo-subleading Voloshin contribution essentially improves the theoretical semileptonic branching ratio of , in agreement with experiment. The semileptonic branching ratios for and are found to be large, i.e., of the order of 20%. The lifetimes hierarchy is in a good qualitative and even quantitative agreement with experiment except for the lifetime, which is somewhat smaller than the experimental value. Future measurements, especially measurements of the semileptonic branching ratios for , and should be decisive for the check of this approach. Received: 29 April 1997 / Revised version: 25 June 1997 / Published online: 20 February 1998     

Studies of intermolecular interactions by matrix isolation vibrational spectroscopy: Self-association of water

The mid- and far-infrared spectra of water in argon and nitrogen matrices have been reinvestigated. The water molecule rotates in an argon matrix, but in a nitrogen matrix two low-frequency bands are attributed to libration of the water monomer about its A and C rotational axes. Combinations of these modes with the stretching and bending modes of the water monomer were observed. A detailed concentration-dependence study enabled bands to be attributed to dimer, trimer, and tetramer or higher multimers. The dimer and trimer were both found to have open chain structures, whereas tetramer or higher multimer species appear to be predominantly cyclic. Intermolecular modes, observed for dimer and trimer in the far-infrared spectra, are tentatively assigned.     

Lateral interactions and zigzag chains of Ho on the Mo(110) surface

The structure of Ho adsorbed layers on the Mo(110) surface has been studied by low energy electron diffraction (LEED) and scanning tunneling microscope (STM). It has been found that at submonolayer coverages Ho atoms, similarly to studied earlier Gd and Nd, form a rich amount of dilute (n × 2) commensurate structures built from zigzag chains oriented along the [11?0] direction. The formation of zigzag chain structures is initiated by the indirect lateral interaction between adsorbed Ho atoms, which, as is illustrated by Monte Carlo simulations, can be well approximated by a screened Coulomb potential superimposed with Friedel oscillations.     

Complex free energies and metastable lifetimes

For two simple models we consider the analytic continuation of the free energy across a first-order phase transition. For each system we also study an associated stochastic dynamics and decay rates for passage to the stable equilibrium. We then investigate the relation between the imaginary part of the free energy and the decay rate per unit volume.Supported in part by U.S.-Israel Binational Science Foundation and by National Science Foundation Grant MCS 77-20683.Alfred P. Sloan Research Fellow. On leave from Indiana University, Bloomington, Indiana.     

Sub-nanosecond lifetimes in Te

The half-lives of the 1776.8 keV 6⁺ level and the 2497.3 keV 7^? level in ¹²⁶Te are measured by registering β-γ coincidences in the decay of ¹²⁶Sb. The results are $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext><mtext>(1776.8)\; =\; 66\pm 3</mtext><mtext>ps</mtext>}}$ and $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext><mtext>(2497.3)\; =\; 152\pm 5\; </mtext><mtext>ps</mtext>}}$. The collective strength of the 6⁺ → 4⁺ transition depopulating the 1776.8 keV state is estimated. An additional half-life of 0.36±0.06 ns is found but not definitely assigned in the level scheme.