Frank-Condon Factors Research Articles

Cooling and trapping of atoms and molecules by counterpropagating pulse trains

We discuss a possible one-dimensional trapping and cooling of atoms and molecules due to their non-resonant interaction with the counter-propagating light pulses trains. The counter-propagating pulses form a one-dimensional trap for atoms and molecules, and properly chosen the carrier frequency detuning from the transition frequency of the atoms or molecules keeps the "temperature" of the atomic or molecular ensemble close to the Doppler cooling limit. The calculation by the Monte-Carlo wave function method is carried out for the two-level and three-level schemes of the atom's and the molecule's interaction with the field, correspondingly. The discussed models are applicable to atoms and molecules with almost diagonal Frank-Condon factor arrays. Illustrative calculations where carried out for ensemble averaged characteristics for sodium atoms and SrF molecules in the trap. Perspective for the nanoparticle light pulses's trap formed by counter-propagating light pulses trains is also discussed.

Metastable excited states of OBr2− and OCl2− dianions

Electronic stabilities, structures, properties, and spectroscopic constants of the halogen oxide dianions OBr2− and OCl2− and their singly charged anions which are of astrophysical and laboratory interests have been studied. The X2Σ states of OBr2− and OCl2− are metastable with PECs having smooth wells with minima located at R=1.859Å and 1.776Å, and Coulomb barriers of 40402.54987cm−1 and 43746.63462cm−1 heights located at RRCB=2.100Å and 1.922Å, respectively, both without any vibrational states. While, the B2Σ state of OBr2− and the A2Σ state of OCl2− are metastable with PECs having wells deep enough to suite several bound states, with minima located at Re=1.773Å and 1.6430Å, and Coulomb barriers of 191437.45813cm−1 and 180550.70294cm−1 heights located at RRCB=2.658Å and 2.4480Å, with De=1.26470eV and 1.60837eV, respectively. The OBr− and OCl− singly charged anions are stable in their ground states. Based on the calculated Frank–Condon factors, it is concluded that metastable excited state OBr2− and OCl2− dianions and ground state OBr− and OCl− singly charged anions can be formed via electron capture processes.

Laser control of atomic and molecular motion by sequences of counterpropagating light pulses

The analysis of atomic motion in the field formed by sequences of counterpropagating light pulses reveals the conditions when the field creates the trap in which the temperature of trapped atoms drops to the Doppler limit. The atomic state is described by the wave function using the Monte Carlo wave function method, whereas the atomic motion is considered in the framework of classical mechanics. Laser cooling and trapping is achieved only for non-resonant atom–field interaction. The pulse area does not matter for this effect, in contrast to the repetition period. When the motion of a trapped atom is slowed down, it oscillates around the anti-nodes of a non-stationary standing wave formed by the counterpropagating light pulses at the point where they ‘collide’. The discussed trap is also applicable for trapping and cooling of the molecules for which the matrix of Frank–Condon factors is almost diagonal.

Multipole analysis of radio-frequency reactions in ultracold atoms

Using the multipole expansion we analyze photo induced reactions in an ultra-cold atomic gas composed of identical neutral bosons. While the Frank-Condon factor dominates the photo induced spin-flip reactions, we have found that for frozen-spin process where the atomic spins are conserved the reaction rate is governed by the monopole $r^2$ and the quadrupole terms. Consequently, the dependence of the frozen-spin reaction rate on the photon wave number $k$ acquires an extra $k^4$ factor in comparison to the spin-flip process. Comparing the relative strength of the $r^2$ and quadrupole modes in dimer photoassociation we predict that the mutual importance of these two modes changes with temperature and scattering length.

Prospects for ultracold carbon via charge exchange reactions and laser cooled carbides

Strategies to produce an ultracold sample of carbon atoms are explored and assessed with the help of quantum chemistry. After a brief discussion of the experimental difficulties using conventional methods, two strategies are investigated. The first attempts to exploit charge exchange reactions between ultracold metal atoms and sympathetically cooled C(+) ions. Ab initio calculations including electron correlation have been conducted on the molecular ions [LiC](+) and [BeC](+) to determine whether alkali or alkaline earth metals are a suitable buffer gas for the formation of C atoms but strong spontaneous radiative charge exchange ensure they are not ideal. The second technique involves the stimulated production of ultracold C atoms from a gas of laser cooled carbides. Calculations on LiC suggest that the alkali carbides are not suitable but the CH radical is a possible laser cooling candidate thanks to very favourable Frank-Condon factors. A scheme based on a four pulse STIRAP excitation pathway to a Feshbach resonance is outlined for the production of atomic fragments with near zero centre of mass velocity.

Theoretical Study of DNA Damage Recognition via Electron Transfer from the [4Fe-4S] Complex of MutY

The mechanism of site-specific recognition of DNA by proteins has been a long-standing issue. The DNA glycosylase MutY, for instance, must find the rare 8-oxoguanine-adenine mismatches among the large number of basepairs in the DNA. This protein has a [4Fe-4S] cluster, which is highly conserved in species as diverse as Escherichia Coli and Homo sapiens. The mixed-valent nature of this cluster suggests that charge transfer may play a role in MutY's function. We have studied the energetics of the charge transfer in Bacillus stearothermophilus MutY-DNA complex using multiscale calculation including density functional theory and molecular dynamics. The [4Fe-4S] cluster in MutY is found to undergo 2+ to 3+ oxidation when coupling to DNA through hole transfer, especially when MutY is near an oxoguanine modified base (oxoG). Employing the Marcus theory for electron transfer, we find near optimal Frank-Condon factors for electron transfer from MutY to oxoguanine modified base. MutY has modest selectivity for oxoguanine over guanine due to the difference in oxidation potential. The tunneling matrix element is significantly reduced with the mutation R149W, whereas the mutation L154F reduces the tunneling matrix element as well as the Frank-Condon factor. Both L154F and R149W mutations are known to dramatically reduce or eliminate repair efficiency. We suggest a scenario where the charge transfer leads to a stabilization of the specific binding conformation, which is likely the recognition mode, thus enabling it to find the damaged site efficiently.

Theoretical study on potential energy curves and spectroscopy properties of ground and low-lying excited electronic states of BrCl+

The calculations on the potential energy curves and spectroscopic constants of the ground and low-lying excited states of BrCl+, one of the important molecular ions in environment science, have been performed by using the multireference configuration interaction method at high level of theory in quantum chemistry. Through analyses of the effects of the spin-orbit coupling interaction on the electronic structures and spectroscopic properties, the multiconfiguration characteristic of the X2Π ground state and low-lying excited states was established. The spin-orbit coupling splitting energy of the X2Π ground state was calculated to be 1814 cm−1, close to the experimental value 2070 cm−1. The spin-orbit coupling splitting energy of the 2Π(II) exited state was predicted to be 766 cm−1. The transition dipole moments and Frank-Condon factors of the 3/2(III)-X3/2 and 1/2(III)-1/2(I) transitions were estimated, and the radiative lifetimes of the two transitions were briefly discussed.

The electronic bands of CrD, CrH, MgD and MgH: application to the ‘deuterium test’

Abstract We compute opacities for the electronic molecular band systems A6Σ+–X6Σ+ of CrH and CrD, and A2Π–X2Σ+ of MgH and MgD. The opacities are computed by making use of existing spectroscopic constants for MgH and CrH. These constants are adjusted for the different reduced masses of MgD and CrD. Frank–Condon factors are used to provide intensities for the individual vibronic bands. These results are used in the computation of synthetic spectra between Teff= 1800 and 1200 K with an emphasis on the realization of ‘deuterium test’, first proposed by Bejar et al. to distinguish brown dwarfs from planetary mass objects. We discuss the possible use of CrD and MgD electronic bands for the ‘deuterium test’. We find CrD to be the more promising of the two deuterides, potentially, the most useful bands of CrH/CrD are the Δv=+1 and Δv=−1 at 0.795 and 0.968 μm.

Spectroscopy of the YbF molecule in low-pressure inductively coupled plasma

The emission spectra of the YbF molecule excited in low-pressure inductively coupled plasma have been recorded for the plasma formed by three different methods. To assign the spectra observed, the quantum-mechanical calculation of the Frank-Condon factors has been performed. The presence of these molecules in the plasma has also been diagnosed experimentally with a monopole mass analyzer.

N - K near-edge x-ray-absorption fine structures of acetonitrile in gas phase

The dynamic processes of N(1s) core-hole excitation in gas-phase CH3CN molecule have been studied at both Hartree-Fock and hybrid density-functional theory levels. The vibrational structure is analyzed for fully optimized core-excited states. Frank-Condon factors are obtained using the linear coupling model for various potential surfaces. It is found that the vibrational profile of the N-K absorption can be largely described by a summation of two vibrational progressions: a structure-rich profile of nu(CN) stretching mode and a large envelope of congestioned vibrational levels related to the strong (-C-CN) terminal bending bond. Excellent agreement between theoretical and experimental spectra is obtained.

Differential cross sections for the electron impact excitation of theAΣu+3,BΠg3,WΔu3,B′Σu−3,a′Σu−1,aΠg1,

Measurements of differential cross sections for the electron-impact excitation of molecular nitrogen from the ground X(sup 1)(Sigma)(sub g)(sup +)(v''=0)level to the A(sup 3)(Sigma)(sub u)(sup +)(v'), B(sup 3)Pi(sub g)(v'), W(sup 3)(Delta)(sub u)(v'),B'(sup 3)(Sigma)(sub u)(sup -)(v'), a(sup 1)(Pi)(sub g)(v'), w(sup 1)(Delta)(sub u)(v'), and C(sup 3)(Pi)(sub u)(v') levels are presented. The data are obtained at the incident energies of 10, 12.5, 15, 17.5, 20, 30, 50, and 100 eV over the angular range of 5(deg)-130(deg) in 5(deg) intervals. The individual electronic state excitation differential cross sections are obtained by unfolding electron energy-loss spectra of molecular nitrogen using available semiempirical Frank-Condon factors. The data are compared to previous measurements and to available theory. We also make several important suggestions regarding future work that, like the present, relies on the unfolding of electron energy-loss spectra for obtaining differential cross sections.

Frank-Condon factors and r-centroids for the B-X bands of 10B18O and 11B18O molecules

Frank?Condon factors and r-centroids have been calculated for the B2?+?X2?+ bands of the 10B18O and 11B18O isotopic molecules assuming that both the B and X states follow a Morse potential curve. The calculated q ?'?" values are compared with observed band intensities and the relationship between the r-centroids and the band positions has been determined and is discussed.

Fourier-transform spectroscopic study of the rotational intensity distribution in the first positive B 3Πg–A 3Σu+ band system of the nitrogen molecule

In the present work we have studied the rotational intensity distribution in the 0–0, 0–1 and 1–3 bands of the B 3 Π g–A 3 Σ u + system of N 2 recorded on a Fourier transform spectrometer. The effective Hamiltonian used by Roux et al. (J. Mol. Spectrosc. 97 (1983) 253) for reduction of the experimental line position data to molecular parameters, is found to be adequate in reproducing the observed line intensities. To enhance the accuracy of the theoretical line intensity calculations, it proved necessary to use rotation-dependent Frank–Condon factor. Using the calculated intensities, it was possible to identify certain rotational lines belonging to the weakest branches Q 13 and Q 31, not reported before.

Lifetime measurement of the A3∏0 electronic state of InCl by laser induced fluorescence

Radiative lifetimes for the A3Π 0 state of InCl have been measured for the first time by laserinduced fluorescence. The collision-free fluorescence radiative lifetime of τ0 7ap; 370ns is proposed for A3Π 0 and a quenching rate constant of k Q≈ 9.87 10-11 cm3 molecule-1 s-1. From the Frank-Condon factors qv'v'' for the v' - v'' transitions and the radiative lifetime τ0 , the electronic transition moment |Re|2 has been obtained.

Lifetime measurement of the A3Π0 electronic state of InCl by laser induced fluorescence

Radiative lifetimes for the A3Π 0 state of InCl have been measured for the first time by laserinduced fluorescence. The collision-free fluorescence radiative lifetime of τ0 7ap; 370ns is proposed for A3Π 0 and a quenching rate constant of k Q≈ 9.87 10-11 cm3 molecule-1 s-1. From the Frank-Condon factors qv'v'' for the v' - v'' transitions and the radiative lifetime τ0 , the electronic transition moment |Re|2 has been obtained.

Chlorophyll a Franck−Condon Factors and Excitation Energy Transfer

The Franck-Condon factors for the S{sub 1}(Q{sub y}) {leftrightarrow} S{sub 0} electronic transition of chlorophyll (Chl) molecules are important for understanding excitation energy transfer in photosynthetic complexes. Currently, there are two sets of Chl a Frank-Condon factors for over 40 modes, one determined by spectral hole burning and the other by fluorescence line narrowing. Those obtained by the latter spectroscopy are, on average, a factor of 30 times smaller than the hole burning values. Nonline-narrowed fluorescence results for the light-harvesting complex 2 of photosystem 2 at 4.2 K are presented that agree quite well with the hole burning but not the fluorescence line narrowing values.

Generalized Morse potential: Symmetry and satellite potentials

We study in detail the bound state spectrum of the generalized Morse potential~(GMP), which was proposed by Deng and Fan as a potential function for diatomic molecules. By connecting the corresponding Schrodinger equation with the Laplace equation on the hyperboloid and the Schrodinger equation for the Poschl-Teller potential, we explain the exact solvability of the problem by an $so(2,2)$ symmetry algebra, and obtain an explicit realization of the latter as $su(1,1) \oplus su(1,1)$. We prove that some of the $so(2,2)$ generators connect among themselves wave functions belonging to different GMP's (called satellite potentials). The conserved quantity is some combination of the potential parameters instead of the level energy, as for potential algebras. Hence, $so(2,2)$ belongs to a new class of symmetry algebras. We also stress the usefulness of our algebraic results for simplifying the calculation of Frank-Condon factors for electromagnetic transitions between rovibrational levels based on different electronic states.

A microscopic theory of desorption induced by electronic transitions

Desorption induced by electronic transitions (DIET) in two cases is investigated from a microscopic point of view. In case A, where a single electron in a state of the localized kind (localized around adsorbates) is excited into a state of the extended kind (extended into the bosom of the substrate), the shape of the excited-state potential-energy surface (PES) may differ markedly from that of the ground-state PES for adsorbate motion. The Franck-Condon factor then takes a finite value, giving rise to a finite desorption probability. In case B, where a single electron in a state of the extended kind is excited into another state of the extended kind, the shape of the excited-state PES is practically the same as that of the ground-state PES. The Frank-Condon factor is then zero. In such a case, one should take DIET as a single-step (coherent) process and take into account the adsorbate-position dependence of the matrix element for state transitions of the electron system in order to obtain a finite desorption probability.

Charge-transfer rate constants for N 2+( ν = 0–4) with Ar at thermal energies

Rate constants for the charge-transfer reaction N 2 +( ν) + Ar → N 2 + Ar + are measured at thermal energies as a function of initial vibrational excitation by laser-induced fluorescence. The reaction is slow for ν = 0, whereas the rate constants for ν = 1–4 are large (≈ 0.5 Langevin rate) and show little dependence on the vibrational level. The rate constants are quantitatively described by a simple model based on energy resonance and a set of modified Frank-Condon factors, which take into account the change in vibrational wave functions of N 2 + and N 2 at short (N 2Ar) + distances.

Factors affecting photoinduced electron transfer in a donor—acceptor pair (DA) incorporated into bovine serum albumin

Abstract A donor—acceptor hybrid molecule (DA) consisting of a 1-dimethyl-aminonaphthalene-5-sulphonate group in an excited singlet state (donor) and a nitroxide radical (acceptor) was incorporated into a hydrophobic cavity of bovine serum albumin (BSA). The kinetics of reversible and irreversible intramolecular electron transfer from the donor to the acceptor were monitored by luminescence and ESR techniques in the temperature range from 77 K to 300 K. The temperature dependence of the micropolarity and the intramolecular dynamics in the vicinity of the donor and the acceptor groups were monitored by fluorescence and ESR techniques, respectively. The Arrhenius dependence of the reversible ET constant ( K e was non-linear and the apparent activation energy ( E app changes from 0 eV (at T =77–100 K) to 0.25 eV (at T =298 K). The temperature region of the E app increase (100–240 K) was close to the temperature of the increase of relaxation shift of the donor luminescent spectra ( T = 100–240 K). On the basis of the obtained kinetic data and of the data of the micropolarity in the vicinity of the donor and the acceptor groups, values of standard Gibbs energy (ΔG 0 ) change, the reorganization energy ( E r , the resonance integral ( V DA ) and the Frank—Condon factor for reversible electron transfer were estimated. The role of molecular dynamics in the vicinity of the donor and the acceptor groups is also discussed.