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The ultrafast nonadiabatic dynamics of a two-electronic-state four-vibrational-mode conical intersection coupled to a finite bath with up to 20 harmonic oscillators has been investigated by employing the multiple Davydov D2ansatz. It is demonstrated, using the multi-configuration time-dependent Hartree method as a benchmark, that this approach provides an efficient and robust description of the internal conversion process at multimode conical intersections. Thanks to the Gaussian nature of the Davydov ansatz, it allows for numerically accurate simulations of time-dependent diabatic and (for the first time for a 24-mode system) adiabatic populations of the electronic states and reduced probability densities of the tuning and coupling modes. The obtained adiabatic populations and wave packets can be used as benchmarks for the testing of various simulation methods, in particular, surface-hopping methods. [ABSTRACT FROM AUTHOR]

Commercially available thallium activated sodium iodide scintillators are typically characterized by a γ-ray energy resolution of 6.5% at 662 keV and a scintillation decay time constant of 230 ns. Energy resolution, non-proportionality, and scintillation decay time are improved when the crystal is co-doped with alkaline earth metals (Sr2+ and Ca2+). The energy resolution of NaI:Tl+ is improved to 5.3%, and the decay time is simultaneously reduced to 170 ns with Sr2+ and Ca2+ co-doping. The improvement in energy resolution, non-proportionality, and decay time are likely due to the suppression of the slow scintillation processes in NaI:Tl+. [ABSTRACT FROM AUTHOR]

Internal conversion is an inherently quantum mechanical process. To date, 'ab initio' computation of internal conversion rates was limited to harmonic based approximations. These are questionable since the typical transition to the ground electronic state occurs at energies which are far from the harmonic limit. It is thus of interest to study the applicability of the Semiclassical Initial Value Representation (SCIVR) approach which is in principle amenable to 'on the fly' studies even with 'many' degrees of freedom. In this work we apply the Herman-Kluk-SCIVR methodology to compute the internal conversion rates for formaldehyde for a variety of initial vibronic states. The SCIVR computation gives reasonable agreement with experiment, while the harmonic approximation typically gives rates that are too high. [ABSTRACT FROM AUTHOR]

Two species that possess different absorption and emission properties have been observed in the low resolution fluorescence excitation spectrum of 5-fluorosalicylic acid (FSA) in the gas phase. The two species were identified as monomer and dimer species using high resolution techniques. Studies of these spectra in the presence of an applied electric field, together with ab initio quantum chemistry calculations, show that the monomer is a 'closed' form of FSA exhibiting an intramolecular C = O···H-O-C hydrogen bond in the ground state. Absorption of light at ∼344 nm transforms this species into the tautomeric form C-O-H···O = C via a barrierless proton transfer process. The large charge rearrangement that accompanies this process results in a significantly red-shifted emission spectrum. The (FSA)2 dimer exhibits two intermolecular C=O...H-O-C hydrogen bonds but in this case the double proton transfer leads to a conical intersection with the ground state and rapid nonradiative decay. The onset of this process and the time scale on which it occurs are revealed by a homogeneous broadening of the dimer's high resolution spectrum. [ABSTRACT FROM AUTHOR]

Spectator resonant KL23L23 Auger electron spectra have been measured in the Si 1s photoexcitation region of Si(CH3)4 using monochromatized undulator radiation combined with a hemispherical electron spectrometer. The broad peak with high intensity in a total ion yield spectrum, coming mainly from excitation of a 1s electron into the 6t2 vacant orbital, induces a spectator Auger decay in which the excited electron remains in its excited orbital. The component on the higher energy side of this peak through 1s excitation into a Rydberg orbital produces resonant Auger decays in which the excited Rydberg electron moves into a slightly higher Rydberg orbital, or is partly shaken up to a significantly higher Rydberg orbital. These findings of Si(CH3)4 indicate a clear contrast to those for SiF4, in which the 1s excitation into a Rydberg orbital induces a shake-down phenomenon as well as a shake-up one. The results of these molecules exhibit a clear splitting effect among excited orbitals which are smeared out by overlapping due to lifetime widths and due to densely populated levels in the 1s electron excitation spectrum. This is consistent with the calculation on photoexcitation within the framework of density functional theory. [ABSTRACT FROM AUTHOR]

In this work single and double ionization spectra of the homo- and heteronuclear argon/krypton dimers and trimers are calculated by means of propagator methods where a four-component implementation was employed for the single ionizations. Scalar relativistic effects play only a minor role for the outer valence spectral structure, whereas spin-orbit coupling and electron correlation have to be treated adequately in order to reproduce the features correctly. Nonradiative decay mechanisms of subvalence vacancies in the argon and krypton dimers and trimers are discussed both for the interatomic Coulombic decay and the electron transfer mediated decay (ETMD). In the heteronuclear triatomic system which serves as a model for larger clusters, a possible ETMD process of the Ar 3s vacancy is found for the linear arrangement of the atoms. In the bent configuration the ETMD channel is closed. [ABSTRACT FROM AUTHOR]

A path integral Monte Carlo method based on the fast-Fourier transform technique combined with the important sampling method is proposed to calculate the decay rate of a metastable quantum system with an arbitrary shape of a potential barrier. The contribution of all fluctuation actions is included which can be used to check the accuracy of the usual steepest-descent approximation, namely, the perturbation expansion of potential. The analytical approximation is found to produce the decay rate of a particle in a cubic potential being about 20% larger than the Monte Carlo data at the crossover temperature. This disagreement increases with increasing complexity of the potential shape. We also demonstrate via Langevin simulation that the postsaddle potential influences strongly upon the classical escape rate. [ABSTRACT FROM AUTHOR]

The photodissociation of DNCN following excitation of the C 2A″←X 2A″ electronic transition was studied using fast beam photofragment translational spectroscopy. Analysis of the time-of-flight distributions reveals a photodissociation channel leading to D+NCN competitive with the previously observed CD+N2 product channel. The translational energy distributions describing the D+NCN channel are peaked at low energy, consistent with internal conversion to the ground state followed by statistical decay and the absence of an exit barrier. The results suggest a relatively facile pathway for the reaction CH+N2→H+NCN that proceeds through the HNCN intermediate and support a recently proposed mechanism for prompt NO production in flames. [ABSTRACT FROM AUTHOR]

Spectroscopic properties have been characterized for trivalent neodymium doped polycrystalline ceramic ytttria, Nd3+:Y2O3. The Judd-Ofelt [Phys. Rev. 127, 750 (1962); J. Chem. Phys. 37, 511 (1962)] analysis has been applied to the room temperature absorption spectrum to determine the radiative decay rates and branching ratios of Nd3+ transitions from the 4F3/2 metastable manifold to the 4IJ lower-lying multiplet manifolds. The quantum efficiency is determined from the measured fluorescence lifetime and the radiative lifetime of the 4F3/2 manifold state. In addition, a detailed characterization of the Stark energy levels of the 4I9/2 and 4I11/2 manifolds has been performed using the room temperature fluorescence spectra for the 4F3/2→4I9/2 and 4F3/2→4I11/2 transitions of Nd3+(4f3) in ceramic Y2O3. The emission cross sections of the 4F3/2→4I9/2 and 4F3/2→4I11/2 intermanifold transitions have been determined. Also, the peak emission cross sections of the principal inter-Stark peak transitions R1→X5 and R1→Y2 have been determined. Finally, the spectroscopic properties of ceramic Nd3+:Y2O3 are compared with those of ceramic Nd3+:YAG as well as single crystals of Nd3+:Y2O3 and Nd3+:YAG. [ABSTRACT FROM AUTHOR]

Singly ionized systems in high-lying energetic final states can stabilize themselves via various electronic decay mechanisms. With increasing system size interatomic and intermolecular processes dominate over intra-atomic (Auger) decay channels. For the small (HI)2 and (LiI)2 clusters fully relativistic ionization spectra are calculated and the subsequent electronic decay of the cations is investigated. Due to the presence of the iodine atom a fully relativistic description is mandatory and was performed by the algebraic diagrammatic construction technique in its four-component form. The lifetimes of the singly ionized final states are estimated by the application of Weisskopf-Wigner [Z. Phys. 63, 54 (1930)] theory. [ABSTRACT FROM AUTHOR]

Time-resolved photoluminescence (PL) near 540 nm, taken from barium titanate (BaTiO3) ultrafine powders of ∼80, 90, and 110 nm in size, was measured at 11 K. Two-exponential functions were found to fit the decay curves well, and the decay lifetimes were composed of one short, about 10 ns, and one long, about 200 ns, time constants, respectively. Results also indicate that the PL peaks show a small blueshift with decreasing BaTiO3 particle size. The decay process consists of the recombination of self-trapped excitons (long lifetime decay) and of the electrons in the surface states with the holes in the valence band (short lifetime decay). The short lifetime component makes comparable contribution to the decay intensity of PL with the long lifetime one. [ABSTRACT FROM AUTHOR]

The constant photocurrent method was implemented to determine the density of states in tritiated hydrogenated amorphous silicon below the Fermi level. The tritiated hydrogenated amorphous silicon samples were grown using a mixture of silane and tritium gases in the dc saddle-field deposition system. Over time the tritium incorporated in the amorphous silicon undergoes beta decay and transmutation into helium. The transmutation leads to an increase in the density of states in the energy gap of the material. These states are linked to silicon dangling-bond defects. Given its well-characterized decay process, tritium can be used as an experimental tool to study the behavior of hydrogenated amorphous silicon thin films as a function of their defect state density. The density-of-states information in this work indicates a dominant peak of doubly occupied dangling bonds (D-) positioned 1.24 eV below the conduction band. The defect density was monitored in time showing an increase of more than two orders of magnitude over a period of 20 days and a decrease of similar magnitude upon thermal annealing. [ABSTRACT FROM AUTHOR]

In a study using time-resolved photoluminescence (PL) to examine the carrier dynamics of a vertically coupled InAs/GaAs quantum dot (QD) of 20 periods, we observed an initial slow carrier decay followed by a fast decay. The time at which the transition from slow to fast decay occurred increased on going to lower QD states at a fixed excitation power, and increased with increasing excitation intensity at a fixed QD state. This behavior is attributed to the relatively efficient vertical transfer of carriers in the vertically coupled InAs/GaAs QD. In addition, this vertical carrier transfer makes the rise of the PL signal slower at lower-energy states. This peculiar carrier dynamics behavior was not observed in a single-layered QD or in a vertically uncoupled QD of 20 periods. [ABSTRACT FROM AUTHOR]

A femtosecond pump-probe technique was employed to study the dissociation dynamics of sulfur dioxide and sulfur dioxide clusters in real time. Dissociation is initiated by a multiphoton scheme that populates the E state. The SO2+ transient is fit to a biexponential decay comprising a fast and a slow component of 230 fs and 8 ps, respectively. The SO+ transient consists of a growth component of 225 fs as well as a subsequent decay of 373 fs. The pump-probe response obtained from the monomer clearly shows the predissociative cleavage of a S–O bond. Upon cluster formation, a sequential increase in the fast decay component is observed for increasing cluster size, extending to 435 fs for (SO2)4+. The transient response of cluster dissociation products SO(SO2)n+, where n=1–3, reflects no growth component indicating that formation proceeds through the ion state. Therefore, cluster formation results in a caging effect, which impedes the dissociation process. Further direct evidence for our proposed mechanism is obtained by a technique that employs a comparison of the amplitude coefficients of each respective component of the fit. This method makes possible the determination of branching ratios of competing relaxation processes and thereby the influence of cluster formation on each can be resolved. The caging effect is attributed to a steric hindrance placed on the SO2 chromophore, preventing it from attaining a linear geometry necessary for dissociation. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In this paper, I consider theoretical models of the decay via photobleaching of a sample of surface-immobilized fluorescent molecules excited by a spatially varying laser intensity profile. I show that, with mild restrictions on the photobleaching mechanism, the fluorescence decay measured in a nonuniform excitation profile is always nonexponential. Under the same conditions, the fluorescence decay can always be approximated by a discrete sum of exponentials. A particular example is given in which a homogeneous population of fluorophores with a single (intensity-dependent) photobleaching lifetime, when illuminated by a Gaussian laser, exhibits power law fluorescence decay at long times. These results indicate that the observation of multiple exponentials in single molecule or ensemble photobleaching lifetime measurements can arise solely as an artifact of a spatially varying laser profile and is not necessarily indicative of heterogeneity in molecular internal states, conformation, or local environment. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The doubly degenerate core-excited Π state of N[sub 2]O splits into two due to the static Renner–Teller effect. The lower state, A[sub 1], has a bent stable geometry and the molecule excited to this state starts to deform itself toward this bent geometry. To probe the effect of the potential energy surfaces of the core-excited A[sub 1] states on the nuclear motion, we measure the momenta of the three atomic ions in coincidence by means of the ion momentum imaging technique. We find that the potential energy surface affects the molecular deformation significantly. N[sub 2]O in the terminal N 1s[sup -1]3πA[sub 1] excited state is observed to be bent more than that in the central N 1s[sup -1]3πA[sub 1] excited state. This means that N[sub 2]O in the terminal N 1s[sup -1]3πA[sub 1] excited state bends faster than that in the central N 1s[sup -1]3πA[sub 1] excited state. When the excitation energy is decreased within the 1s[sup -1]3π resonances, the nuclear motion in the A[sub 1] states becomes faster. This is interpreted by the notion that the excitation occurs onto the steeper slope part of the potential energy surface of the excited state for the lower excitation energy. The branching ratio of the A[sub 1] excitation increases with the decrease in the excitation energy. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Ab initio calculations on the heterodimer C[sub 8]H[sub 6]NH...NH[sub 3] are carried out for its ground, the excited πσ[sup *], and the ground cationic electronic states, enabling the description of hydrogen or proton transfer, respectively. Two-dimensional quantum-dynamical computations on the πσ[sup *] potential surface help one to understand the mechanism and the time scale of the hydrogen transfer. Subsequent decay processes are discussed depending on the vibrational excitation of the ammonium constituent. Finally, the theoretical results obtained are used for the interpretation of the time-dependent signals observed in femtosecond pump–probe experiments. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The feasibility of efficient population transfer between an initial state and a decaying target state of the same parity without populating an intermediate state, in the presence of large-amplitude stochastic energy level fluctuations that mimic the dephasing in a solute molecule due to the influence of a solvent, is demonstrated theoretically. In particular, it is shown that a decaying target state, whose decay rate constant is large compared with the band width of picosecond laser pulses but small compared with the associated peak Rabi frequencies, can dramatically suppress the dephasing-induced nonadiabaticity associated with the dynamics of population transfer, resulting in, irrespective of the correlation time of stochastic energy level fluctuations, negligible population in the intermediate state and complete population transfer to the decaying target state. These results should further motivate experimental studies of optical control of molecular dynamics in a liquid. An interesting connection between our results and the quantum Zeno and anti-Zeno effects is also discussed. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Transport properties including collective and tracer diffusivities of nitrogen, modeled as a diatomic molecule, in single walled carbon nanotubes have been studied by equilibrium molecular dynamics at different temperatures and as a function of pressure. It is shown that while the asymptotic decay of the translational and rotational velocity autocorrelation function is algebraic, the collective velocity decays exponentially with the relaxation time related to the interfacial friction. The tracer diffusivity in the nanochannel, which is comparable in magnitude with diffusivity in the equilibrium bulk phase, depends only weakly on the conditions at the fluid–solid interface, whereas the collective diffusivity is a strong function of the hydrodynamic boundary conditions and is found to be three orders of magnitude higher than self-diffusivity in carbon nanotubes and for the comparatively rough surface of the rare-gas tube it is one order of magnitude greater. A relationship between the collective diffusivity and the Maxwell coefficient describing wall collisions is obtained. The transport coefficients appear to be insensitive to the long-range details of the potential function. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A hole in a 4d orbital of atomic xenon relaxes through Auger decay after a lifetime of 3 fs. Adding electronegative fluorine ligands to form xenon fluoride molecules, results in withdrawal of valence-electron density from Xe. Thus, within the one-center picture of Auger decay, a lowered Xe 4d Auger width would be expected, in contradiction, however, with experiment. Employing extensive ab initio calculations within the framework of many-body Green’s functions, we determine all available decay channels in XeF[sub n] and characterize these channels by means of a two-hole population analysis. We derive a relation between two-hole population numbers and partial Auger widths. On this basis, interatomic electronic decay processes are demonstrated to be so strong in the xenon fluorides that they overcompensate the reduction in intra-atomic Auger width and lead to the experimentally observed trend. The nature of the relevant processes is discussed. These processes presumably underlie Auger decay in a variety of systems. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The vacuum ultraviolet pulsed field ionization (PFI)-photoelectron (PFI-PE) spectrum of CO[sub 2] has been measured in the energy region of 19.0-20.0 eV. The PFI-PE vibrational bands resolved for CO[sup +, sub 2] are overwhelmingly dominated by the origin band along with weak vibrational bands corresponding to excitations of the v[sup +, sub 1] (symmetric stretching), v[sup +, sub 2] (bending), and v[sup +, sub 3] (antisymmetric stretching) modes. The simulation of the rotational contour resolved in the origin PFI-PE band yields a value of 19.3911±0.0005 eV for the ionization energy of CO[sub 2] to form CO[sup +, sub 2](C [sup 2]&Zigma;[sup +, sub g])./ A PFI-PE peak is found to coincide with each of the 0 K dissociation thresholds for the formation of O[sup +]([sup 4]S) + CO(X [sup 1]&Zigma;[sup +]) and CO[sup +] (X ²&Zigma;[sup +] ) +O(³P). This observation is tentatively interpreted to result from the lifetime switching effect, arising from the prompt dissociation of excited CO[sub 2] in high-n (n ≥ 100) Rydberg states prior to PFI. We have also examined the decay pathways for state-selected CO[sup +, sub 2] in the internal energy range of 5.2-6.2 eV using the PFI-PE-photoion coincidence scheme. The coincidence TOF data show unambiguously the formation of O[sup +]([sup 4]S) + CO(X 1&Zigma;[sup +]; v″ = 0,1) and CO[sup +](X ²&Zigma;[sup +] ; v[sup +] = 0,1) + O(³P). Analysis of the kinetic energy releases of fragment ions suggests that the dissociation of excited CO[sup +, sub 2] involved is nonstatistical and proceeds with an impulsive mechanism. Potential energy functions (PEFs) for the CO[sup +, sub 2] (C ²&Zigma;[sup +, sub g]) state and the lowest quartet states of CO[sup +, sub 2], together with their spin-orbit interactions, have been calculated using the complete active space self-consistent field and internal contracted multireference configuration... [ABSTRACT FROM AUTHOR]

We present correlated measurements of radioluminescence, photoluminescence, and thermoluminescence, as well as the measurements of decay kinetics both under ultraviolet and [sup 22]Na(511 keV) photon excitations for Mo-doped and doubly (Mo,Y)-doped PbWO[sub 4] single crystals. A wide concentration range of Mo doping (200-50 000 ppm) is covered. Y codoping results in significant suppression of trapping states induced by the Mo doping. Consequently, an improvement of temporal characteristics, such as acceleration of the scintillation decay process, of doubly doped material with respect to Y-free crystals, is achieved. For the optimum Mo concentration (275010 000 ppm), the temporal characteristics are fully comparable to an undoped PbWO[sub 4], while the light yield is increased by a factor of 2.2. [ABSTRACT FROM AUTHOR]

Dipolar effects in solution nuclear magnetic resonance lead to additional peaks in two-dimensional experiments. These peaks, which have the experimental properties of intermolecular multiple-quantum coherences, have been used in a variety of applications. Most efforts have focused on intermolecular zero-quantum or double-quantum coherences, which originate in two-spin terms from the equilibrium density matrix. In this paper, we characterize the “third-order experiments” (Hahn echo decay and triple-quantum CRAZED, which both originate in the three-spin terms in the equilibrium density matrix) both theoretically and experimentally. For example, in the coupled-spin picture, Hahn echo decays in concentrated solutions arise initially from intermolecular, 3-spin, -1-quantum coherences, which are partially converted to 3-spin, +1-quantum coherences by the second pulse, and hence survive the 1:1 coherence transfer echo. Such terms require two dipolar couplings to become observable. We discuss the general properties of both of these sequences, and show that they only give information that is already present in the “second-order” double-quantum and zero-quantum experiments. Finally, we also show that relaxation and diffusion can be introduced into the coupled-spin picture in a straightforward manner. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Aging behavior of red, green, and blue photoluminescence from porous silicon formed by electrochemical etching aided with zinc has been studied over a 3 month time span. Time-resolved photoluminescence spectra and decay dynamics have revealed that there are two radiating states in Zn-aided porous silicon. One is the quantum confinement and the other is the oxygen-related defect. For green emission, the wavelength shifts from 520 to 420 nm and its photoluminescence spectra and decay behavior become very similar to those of blue emission. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have studied the yield and the time evolution of pulsed laser induced photoluminescence in proton irradiated and thermally annealed amorphous hydrogenated silicon carbon alloys prepared by plasma enhanced chemical vapor deposition. Three major fluorescence decay channels have been observed with decay rates independent from proton irradiation and thermal annealing. Lack of correlation between yield and average decay time suggests a very simple phenomenological model which allows evaluation of the nonradiative time constant which is found to be linearly correlated with the photoluminescence yield. Our model suggests that radiative recombination occurs via exciton decay while the nonradiative recombination is driven by the trapping of carriers in defects states. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Examines the role of Sano's decay curve in the reduction of precursor decay anomaly in single crystal lithium fluoride. Quantitative analysis of strain, particle, velocity and stress in a precursor; Existence of degenerate contraction and subrarefraction waves; Derivation of the inequalities relating decay rates; Reduction of plastic strain rates.

Provides information on a study regarding the reduction of precursor decay anomaly in single-crystal lithium fluoride (LiF) using a macroscopic approach. Piezoelectric current from shock-loaded quartz; Formulation of unsteady wave fronts; Prediction of unsteady wave front near impact surface.

Studies the spin-forbidden predissociation reaction of the ground state N[sub 2]O by quantum dynamics calculations. Obtaining of the potential energy surfaces of the singlet ground state of the N[sub 2]O and three triplet ones; Estimation of the decay rate of individual singlet vibrational state.

Highlights • High resolution analysis of AlD+ (A2Π - X 2 Σ +) FTS spectra. • Improved molecular constants of the X 2 Σ + state of AlD+. • Experimental and theoretical study of the Λ-doubling of the A2Π v=0,1 levels. • Spin-orbit potentials to the first two atomic limits. • Calculated lifetimes and branching ratios for the A2Π and B 2 Σ + states of AlD +. Graphical abstract Abstract The spectrum of the AlD + isotopologue has been investigated at high resolution in the 27 , 000 − 29 , 000 cm − 1 region using a Fourier transform emission spectroscopy technique. The AlD + molecules were produced within a water-cooled aluminum hollow-cathode lamp in the presence of 1.5 Torr of Ne and 0.8 Torr of ND 3. The (0, 0) and (1, 1) bands belonging to the A 2 Π − X 2 Σ + system were recorded with an instrumental resolution of 0.03 cm − 1. In total, almost 500 rotational frequencies were measured with an absolute accuracy of about 0.005 cm − 1. It improved the experimental accuracy of the determined frequencies by the factor 10 compared to the previous work [J Phys B: Mol Phys 1984;17:L861-L866]. The rotational analysis has shown irregularities in the Λ − doubling splitting of the A2Π v = 0 , 1. Consequently, the A2Π state has been represented by the rotational term values, while the regular X 2 Σ + state by the molecular constants. The causes of the irregularities were identified in the interaction between the A2Π and the B 2 Σ + states, which lies about 3720 cm − 1 above. Supporting ab initio quantum chemical calculations, including spin-orbit effects, reproduce the observed spectroscopic constants including the small energy splittings due to spin-rotation interactions (for 2 Σ + states) and Λ − doubling. [ABSTRACT FROM AUTHOR]

We consider a model of an unstable state defined by the truncated Breit-Wigner energy density distribution function. An analytical form of the survival amplitude a(t) of the state considered is found. Our attention is focused on the late time properties of a(t) and on effects generated by the non-exponential behavior of this amplitude in the late time region: In 1957, Khalfin proved that this amplitude tends to zero as t goes to the infinity more slowly than any exponential function of t. This effect can be described using a time-dependent decay rate γ(t), and then the Khalfin result means that this γ(t) is not a constant but at late times, it tends to zero as t goes to the infinity. It appears that the energy E(t) of the unstable state behaves similarly: It tends to the minimal energy Emin of the system as t → ∞. Within the model considered, we find two first leading time-dependent elements of late time asymptotic expansions of E(t) and γ(t). We discuss also possible implications of such a late time asymptotic properties of E(t) and (t) and cases where these properties may manifest themselves. [ABSTRACT FROM AUTHOR]

Motivated by recent R D , R D ⁎ and R J / ψ anomalies in B → D ℓ − ν ¯ ℓ , B → D ⁎ ℓ − ν ¯ ℓ and B c → J / ψ ℓ − ν ¯ ℓ decays, respectively, we study possible R-parity violating supersymmetric effects in B c → J / ψ ℓ − ν ¯ ℓ , η c ℓ − ν ¯ ℓ and Λ b → Λ c ℓ − ν ¯ ℓ decays, which are also induced by b → c ℓ − ν ¯ ℓ at quark level. We find that (I) the constrained slepton exchange couplings λ i 33 λ ˜ i 23 ′ ⁎ involving in b → c τ − ν ¯ τ transition from relevant latest experimental data still have quite large effects on all (differential) branching ratios and the normalized forward–backward asymmetries of the exclusive semileptonic b → c τ − ν ¯ τ decays as well as the ratios of the (differential) branching ratios; (II) after satisfying the data of R D and R D ⁎ , the upper limit of R J / ψ , R η c and R Λ c could be increased by 10%, 112% and 24%, respectively, from their upper limits of the Standard Model predictions by the λ i 33 λ ˜ ′ ⁎ i 23 couplings. The results in this work could be used to probe R-parity violating effects and will correlate with searches for direct supersymmetric signals at the running LHCb and the forthcoming Belle-II. [ABSTRACT FROM AUTHOR]

The optical emission study of aluminum (Al) plasma generated by a $Q$ -switched Nd:YAG laser has been presented. The plasma parameter, such as electron temperature ($T_{e}$) and electron number density ($N_{e}$), has been estimated. The electron temperature has been estimated by four different methods and $N_{e}$ was estimated by Stark broadening of spectral lines and the Saha–Boltzmann equation. The laser-generated Al plasma was optically thin and also fulfills the conditions of local thermodynamical equilibrium. The emission spectrum used for determination of the branching fraction and thus transition probabilities of all allowed transitions. The measured values are good in agreement with the literature. [ABSTRACT FROM AUTHOR]

Examines the stability and decay of hydrogen, deuterium, and nitrogen atoms in frozen ammonia. Factor contributing to the residual differences in the atomic spectra; Establishment of the presence of hydrogen and deuterium atoms by observation of resonances at magnetic field strengths; Details on the splitting of the nitrogen atom doublet.

Examines the time-resolved fluorescence spectroscopy of Zinc-tetraphenylporphyrin (ZnTPP) in high-lying electronic states. Role of up-conversion technique in measuring ZnTPP; Details on depopulation using the vibrational states; Relevance of rotational diffusion in anisotropy decay.

Discusses dipole-dipole interaction and anisotropy effects in the itinerant oscillator model. How decay modes of the tagged molecule and its surroundings may be decoupled for rotation in space; Possibility in the electric polarization of the itinerant oscillator; General separation procedure for inertial response; Inertial effects in the motion of a rigid body in space.

Discusses the application of electronic structure methods and nonperturbative resonance theory to study the radiative and radiationless decay mechanisms of the magnesium bromide vibrational levels. Characterization of the adiabatic electronic states; Modification of the nonrelativistic potential energy curves in the first order degenerate perturbation theory.

The description of resonances originating from several coupled electronic states in a diabatic or approximate diabatic basis can offer both conceptual insights and computational challenges. In a three-state problem, two bound electronic states strongly coupled to a single dissociative continuum, large resonance energy shifts (thousands of cm-1), and linewidths varying over 4 orders of magnitude can be encountered. In this work a nonperturbative computational approach is developed to treat this class of resonances. Expressions for both the radiative and radiationless decay rates are developed. Although the approach is nonperturbative, the linewidth is expressed in a Golden-Rule-type formula. The resonance energy is obtained from the iterative solution of an eigenvalue problem in the bound state space. These attributes enable efficient determination both narrow and broad linewidths and large resonance energy shifts. The approach is used to characterize both radiative and radiationless decay of the 2,3 3Πg states of Al2 using a rigorous three-state diabatic basis. Lifetimes ranging from tenths of picoseconds to nanoseconds are determined. The corresponding resonance energy shifts are on the order of 4000 cm-1. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The decay of the excited singlet state of an aromatic molecule such as naphthalene adsorbed to the surface of silica is nonexponential. This nonexponential decay is shown to result from a multipolar interaction between the excited adsorbate and the intrinsic defects of silica. We present experimental evidence for direct energy transfer between the donor molecules, naphthalene and 2-methoxynaphthalene, and acceptor defects sites of a crystalline silica zeloite (silicalite). The principal condition for direct energy transfer, spectral overlap between the optical absorption of the defects and the fluorescence emission of the adsorbate is demonstrated for this system, and the nonexponential relaxation of the donor is shown to be described by a Forster-type stretched exponential. Based on the spectral overlap and energy transfer rate determined, the intrinsic defect density of silicalite is calculated to be 3±2×1020 cm-3. [ABSTRACT FROM AUTHOR]

Calculations of the total and partial decay widths are presented for the vibrational predissociation of H2HF. The calculation is done for the total angular momentum J=0 of the molecule and for the dissociation process H2HF(v=1)→H2(v=0)+HF(v=0). A time-dependent golden rule wave packet method is employed in the numerical calculation for the decay widths. The lifetime of the complex is determined from our calculation to be about 600 ns for para- and 1600 ns for ortho-H2HF. These values are much larger than the experimentally measured value of 27 ns for ortho-H2HF. The large discrepancy in lifetime for H2HF is in sharp contrast to the excellent agreement in lifetime for D2HF between theory and experiment, though the same potential energy surface is used in both calculations. We also present the rotational state distribution of the fragments H2 and HF following the vibrational predissociation of H2HF. It is found that about 58% of the final rotational population is in j=4 states of H2 for para-H2HF and about 48% is in j=5 states of H2 for ortho-H2HF. [ABSTRACT FROM AUTHOR]

We have measured the decay rates of optically excited triplet states of pyrazine and methylpyrazine in a supersonic jet. The excess vibrational energy dependence of the radiationless rate constants in the energy range between the T1 and the S1 electronic origins of the isolated molecules was explored. Decay rates between 5×102 and 105 s-1 were found in the 1800 cm-1 range of excess vibrational energy above the origin of the T1 state in pyrazine. In methylpyrazine the decay rates increase from 8×102 to 3.3×104 in the first 600 cm-1 excess energy range above the T1 origin. The decay rates are free of mode specificity and rotational effects. The wide dynamic range of the T1→S0 radiationless rates of pyrazine is substantially enhanced by methyl substitution. The results support a model which suggests that certain vibrational modes, those which undergo large frequency decreases in the excited state, control the strong vibrational energy dependence of the T1→S0 intersystem crossing of pyrazine. These large frequency changes result from the interaction of the near lying 3nπ* and 3ππ* states (the ‘‘proximity effect’’). The enhancement of the excess energy dependence of the decay rates by methyl substitution indicates a further decrease in the frequency of these modes. This effect of the methyl group is consistent with the ‘‘proximity effect.’’ The frequency reduction of these modes in the S1 manifold of methylpyrazine also support this mechanism. [ABSTRACT FROM AUTHOR]

Fluorescence upconversion was used to measure the time evolution of the fluorescence anisotropy of aniline in three hydrocarbon, alcohol, and aprotic polar solvents. The deconvoluted anisotropy decay time of 0.94±0.05 ps in aniline/isopentane solution is only 54% longer than calculated for free rotation of collision-free molecules, and increasing the solvent viscosity by a factor of 15 by going from isopentane to hexadecane increases the rotational relaxation time by only another 70% to 1.6 ps. The extended diffusion theory applied to the aniline/isopentane anisotropy decay resulted in a collisional time of 205±15 fs, implying that electronically excited aniline in this hydrocarbon rotates on average 19.5±1.5 deg between collisions. These results indicate that the orientational motion of electronically excited aniline in isopentane is significantly nondiffusive. The anisotropy decayed much more slowly in methanol and acetonitrile than in the hydrocarbons, presumably due to dipole–dipole interactions in acetonitrile and/or hydrogen bonding interactions in the hydroxylic solvent. The anisotropy decay in methanol presented double exponential behavior, probably due either to the coexistence of two slowly interconverting aniline species (hydrogen and nonhydrogen bonded) in solution or to a fast contribution from the hydrogen-bonded aniline molecules rotating around their long axes. Free rotation, hydrodynamic models, extended diffusion, and Langevin calculations were used to evaluate the results and comparisons were made among the various approaches. [ABSTRACT FROM AUTHOR]

Presents a study which proposed a characteristics scheme to compute the flow field behind the elastic precursor in plane impact. Features of the scheme; Effects of flow field on the resolution of precursor decay anomaly; Formulation of equations.

Describes a computer-based evaluation method which allows one to resolve rapid decay rates and to separate different decay mechanisms contributing to data from optical pump-probe experiments. Calculation of the carrier density; Polarization of the pump beam; Carrier recombination mechanisms for the semiconductors.

Investigates the cause of the precursor decay anomaly in lithium fluoride single crystals based on the stress-time profiles. Discussion on the attenuation process; Equation for the stress relaxation function; Derivation and evaluation of inequalities.

Focuses on a study which measured the distribution of chromophore sites in a dye-doped polymer in terms of decay rate and breadth parameter. Theoretical model; Experimental procedure; Results and discussion; Conclusion.

The nonradiative decay channels of the valence electronic states of the gas-phase tetrahedral ions CF+4, SiF+4, CCl+4, SiCl+4, and GeCl+4 have been studied in the range 35–100 nm by a novel form of photoionization mass spectrometry. Tunable vacuum UV radiation from a synchrotron source ionizes the parent neutral molecule, and electrons and ions are detected by the photoelectron–photoion coincidence technique. The experiment is repeated continuously as a function of photon energy, and a three-dimensional histogram of photon energy versus ion time of flight versus coincidence count rate is produced. By taking cuts through this histogram, photoionization curves for the different fragment ions can be extracted. The appearance energies of the fragment ions (e.g., CF+2 from CF4, CCl+ from CCl4) occur at the adiabatic ionization potential of an electronic state of the parent ion, and not at the thermodynamic appearance energy of that ion. Attempts to measure the kinetic-energy releases in the fragmentation pathways have only been partially successful. The results are complementary to those of recent experiments to probe the radiative decay of these electronic states of MX+4 [M=C, Si, Ge; X=F, Cl] [J. Chem. Phys. 89, 2675 (1988); 89, 2683 (1988)], where the C 2T2 and D 2A1 third and fourth excited electronic states can show radiative decay to a surprising degree. The decay dynamics of the C and D states of MX+4 are reviewed. In general, the fluorides show different behavior to the analogous chlorides, and the carbon species behaves differently to the corresponding silicon or germanium species. [ABSTRACT FROM AUTHOR]