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28 Jun 2006

Volume 124, Issue 24, Articles (24xxxx)

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Infrared intensity in small ammonia and water clusters

Mikhail N. Slipchenko, Kirill E. Kuyanov, Boris G. Sartakov, and Andrey F. Vilesov

J. Chem. Phys. 124, 241101 (2006); http://dx.doi.org/10.1063/1.2216712 (4 pages) | Cited 31 times

Online Publication Date: 23 June 2006

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Helium droplet technique has been used in order to measure the strength of the infrared absorption in small ammonia and water clusters as a function of size. Hydrogen bonding in ammonia and water dimers causes an enhancement of the intensity of the hydrogen stretching bands by a factor of four and three, respectively. Two types of the hydrogen bonded clusters show different size dependence of the infrared intensity per hydrogen bond. In ammonia (NH3)2 and (NH3)3 it is close to the crystal value. In water clusters, it increases monotonically with cluster size being in tetramers, a factor of two smaller than in the ice. The measured infrared intensity in water clusters is found to be a factor of two to three smaller as compared to the results of numerical calculations.
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36.40.Mr Spectroscopy and geometrical structure of clusters
33.20.Ea Infrared spectra
33.70.Fd Absolute and relative line and band intensities
33.15.Fm Bond strengths, dissociation energies

Direct observation of the transition state of ultrafast electron transfer reaction of a radiosensitizing drug bromodeoxyuridine

C.-R. Wang, A. Hu, and Q.-B. Lu

J. Chem. Phys. 124, 241102 (2006); http://dx.doi.org/10.1063/1.2217014 (4 pages) | Cited 13 times

Online Publication Date: 26 June 2006

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Replacement of thymidine in DNA by bromodeoxyuridine (BrdU) has long been known to enhance DNA damage and cell death induced by ionizing/UV radiation, but the mechanism of action of BrdU at the molecular level is poor understood. Using time-resolved femtosecond laser spectroscopy, we obtain the real-time observation of the transition state of the ultrafast electron transfer (ET) reaction of BrdU with the precursor to the hydrated electron, which is a general product in ionizing/UV radiation. The results show that the ET reaction is completed within 0.2 picosecond (ps) after the electronic excitation, leading to the formation of a transition state BrdU*− with a lifetime of ∼ 1.5 ps that then dissociates into Br− and a high reactive radical dU*. The present results can greatly enhance our understanding not only of the mechanism of BrdU as a radio-/photosensitizer but of the role of prehydrated electrons in electron-initiated processes in biological and environmental systems.
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82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
82.53.Ps Femtosecond probing of biological molecules
87.15.R- Reactions and kinetics
87.15.M- Spectra of biomolecules
87.53.-j Effects of ionizing radiation on biological systems

Complete infrared spectroscopic characterization of phenol-borane-trimethylamine dihydrogen-bonded complex in the gas phase

G. Naresh Patwari, Asuka Fujii, and Naohiko Mikami

J. Chem. Phys. 124, 241103 (2006); http://dx.doi.org/10.1063/1.2212937 (4 pages) | Cited 9 times

Online Publication Date: 26 June 2006

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In the paper we report the first observation of the vibrational spectrum in the B–H stretching region in the gas phase for a dihydrogen bonded complex. The appearance of three transitions for the B–H stretching modes of a (di)hydrogen-bonded complex involving borane-trimethylamine indicates the lowering of the symmetry on the BH3 group upon interaction with phenol. Further, the shift in the O–H stretching frequency indicates that phenol is hydrogen bonded to borane-trimethylamine. The two sets of the present data establish, unequivocally, the formation of O–H⋯H–B dihydrogen-bonded complex between phenol and borane-trimethylamine.
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33.20.Ea Infrared spectra
33.20.Tp Vibrational analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.15.Fm Bond strengths, dissociation energies
33.70.Jg Line and band widths, shapes, and shifts

Adsorption of colloidal particles to curved interfaces

S. Komura, Y. Hirose, and Y. Nonomura

J. Chem. Phys. 124, 241104 (2006); http://dx.doi.org/10.1063/1.2216697 (4 pages) | Cited 7 times

Online Publication Date: 27 June 2006

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As a simple model for a Pickering emulsion droplet, we consider the adsorption of spherical particles to a spherical liquid-liquid interface in order to investigate the curvature effect on the particle adsorption. By taking into account both the surface and the volume energies due to the presence of a particle, we show that the equilibrium contact angle is determined by the classical Young’s equation although the adsorption energy depends on the curvature. We also calculate the partitioning of the colloidal particles among the two liquids and the interface. The distribution of colloidal particles is expressed in terms of the interfacial curvature as well as the relative wettability of the particle.
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68.05.-n Liquid-liquid interfaces
68.43.Mn Adsorption kinetics
68.03.Cd Surface tension and related phenomena
82.70.Dd Colloids
82.70.Kj Emulsions and suspensions

Observing the stereodynamics of chemical reactions using randomly oriented molecular beams

Magnus Gustafsson, Rex T. Skodje, Jianyang Zhang, Dongxu Dai, Steven A. Harich, Xiuyan Wang, and Xueming Yang

J. Chem. Phys. 124, 241105 (2006); http://dx.doi.org/10.1063/1.2217015 (4 pages) | Cited 6 times

Online Publication Date: 28 June 2006

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A new method is demonstrated to study the stereodynamics of simple chemical reactions that does not require the use of oriented (or aligned) molecular beams or measurements of the orientation state of product molecules. Instead, it is shown that by numerically combining accurate measurements of the state-to-state differential cross section for two or more rotational states of the reagent molecule, the separate contribution from the individual helicity states can be extracted. New molecular beam experiments are conducted for the D+H2→HD+H reaction that confirm the validity of the method.
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82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.20.Hf Product distribution

The heat of formation of chlorine-isocyanate and the relative stability of isoelectronic molecules: An experimental and theoretical study

Yuanyuan Ji, Petia Bobadova-Parvanova, Chris Larson, Peter C. Samartzis, Keiji Morokuma, Jim Jr-Min Lin, Tao-Tsung Ching, Chanchal Chaudhuri, Shih-Huang Lee, and Alec M. Wodtke

J. Chem. Phys. 124, 241106 (2006); http://dx.doi.org/10.1063/1.2210934 (5 pages) | Cited 1 time

Online Publication Date: 29 June 2006

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Accurate thermochemical data of small molecules are invaluable to the progress of every aspect of chemistry, especially in the atmosphere, combustion and industry. In this work, photofragmentation translational spectroscopy and 1st principles electronic structure theory reveal the literature value of the heat of formation of chlorine-isocyanate to be in error by more than 40 kcal/mol. We report a revised experimental value for D0(Cl–NCO) = 51±3 kcal/mol which leads to a ΔHf (ClNCO) = 8.5±3 kcal/mol. High level ab initio (CCSD(T)) electronic structure calculations extrapolated to the complete basis set limit give D0(Cl–NCO) = 56.3 kcal/mol, in good agreement with experiment. In light of the present results, the destabilization of azides relative to isoelectronic isocyanates has been evaluated empirically for three pairs of related molecules. It is found to be 90–110 kcal/mol, and has been attributed mainly to the weakening of the N–NN bond relative to the N–CO bond. Electronic structure calculations employing decomposition analysis suggest that, compared to homopolar N2, the math π polarity provides better orbital interaction (charge transfer) and electrostatic attraction and results in a closer encounter and larger stabilization between the fragments and that this is the origin of isoelectronic destabilization of azides relative to the isocyanates.
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82.60.Cx Enthalpies of combustion, reaction, and formation
82.50.Hp Processes caused by visible and UV light
82.20.Db Transition state theory and statistical theories of rate constants
82.20.Hf Product distribution
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
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back to top Theoretical Methods and Algorithms

Comparison of overlap-based models for approximating the exchange-repulsion energy

Pär Söderhjelm, Gunnar Karlström, and Ulf Ryde

J. Chem. Phys. 124, 244101 (2006); http://dx.doi.org/10.1063/1.2206182 (10 pages) | Cited 8 times

Online Publication Date: 23 June 2006

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Different ways of approximating the exchange-repulsion energy with a classical potential function have been investigated by fitting various expressions to the exact exchange-repulsion energy for a large set of molecular dimers. The expressions involve either the orbital overlap or the electron-density overlap. For comparison, the parameter-free exchange-repulsion model of the effective fragment potential (EFP) is also evaluated. The results show that exchange-repulsion energy is nearly proportional to both the orbital overlap and the density overlap. For accurate results, a distance-dependent correction is needed in both cases. If few parameters are desired, orbital overlap is superior to density overlap, but the fit to density overlap can be significantly improved by introducing more parameters. The EFP performs well, except for delocalized π systems. However, an overlap expression with a few parameters seems to be slightly more accurate and considerably easier to approximate.
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31.15.-p Calculations and mathematical techniques in atomic and molecular physics
34.20.Gj Intermolecular and atom-molecule potentials and forces

Hybrid quantum/classical molecular dynamics for a proton transfer reaction coupled to a dissipative bath

Soo Young Kim and Sharon Hammes-Schiffer

J. Chem. Phys. 124, 244102 (2006); http://dx.doi.org/10.1063/1.2206175 (12 pages) | Cited 12 times

Online Publication Date: 26 June 2006

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A hybrid quantum/classical molecular dynamics approach is applied to a proton transfer reaction represented by a symmetric double well system coupled to a dissipative bath. In this approach, the proton is treated quantum mechanically and all bath modes are treated classically. The transition state theory rate constant is obtained from the potential of mean force, which is generated along a collective reaction coordinate with umbrella sampling techniques. The transmission coefficient, which accounts for dynamical recrossings of the dividing surface, is calculated with a reactive flux approach combined with the molecular dynamics with quantum transitions surface hopping method. The hybrid quantum/classical results agree well with numerically exact results in the spatial-diffusion-controlled regime, which is most relevant for proton transfer in proteins. This hybrid quantum/classical approach has already been shown to be computationally practical for studying proton transfer in large biological systems. These results have important implications for future applications to hydrogen transfer reactions in solution and proteins.
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82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
82.20.Db Transition state theory and statistical theories of rate constants
87.14.E- Proteins
82.39.Jn Charge (electron, proton) transfer in biological systems
87.15.R- Reactions and kinetics

On the characterization of three state conical intersections using a group homomorphism approach: Mapping the full N−5 dimensional seam space

Michael S. Schuurman and David R. Yarkony

J. Chem. Phys. 124, 244103 (2006); http://dx.doi.org/10.1063/1.2206185 (11 pages) | Cited 8 times

Online Publication Date: 28 June 2006

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A method for characterizing the degeneracy preserving seam space in the vicinity of a three state conical intersection is introduced. Second order degenerate perturbation theory is used to construct an approximately diabatic Hamiltonian whose eigenenergies and eigenstates accurately describe the vicinity of the three state conical intersection in its full dimensionality. The perturbative analysis enables the large number, 6(Nint(Nint+1)/2), of unique second order parameters needed to construct this accurate Hamiltonian to be determined from ab initio data at a limited number of nuclear configurations, with (Nint+10) being minimal. Using the minimum energy three state conical intersection of the pyrazolyl radical (Nint = 18), the potential of this approach is illustrated. A Hamiltonian comprised of the ten characteristic (linear) parameters and over 1440 second order parameters is constructed and used to determine the locus of the conical intersection seam as well as to describe the 18 dimensional space in the vicinity of that point of intersection. Our results demonstrate the ability of this methodology to quantitatively reproduce the ab initio potential energy surfaces near a three state conical intersection.
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31.15.xp Perturbation theory
31.15.A- Ab initio calculations
31.50.-x Potential energy surfaces

The effects of geometry on the hyperpolarizability

Mark G. Kuzyk and David S. Watkins

J. Chem. Phys. 124, 244104 (2006); http://dx.doi.org/10.1063/1.2205859 (9 pages) | Cited 19 times

Online Publication Date: 30 June 2006

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Extensive studies in the past have focused on precise calculations of the nonlinear-optical susceptibility of thousands of molecules. In this work, we use the broader approach of considering how geometry and symmetry alone play a role, irrespective of molecular constraints. We investigate the nonlinear optical response of potential energy functions that are given by a superposition of force centers (representing the nuclear charges) that lie in various planar geometrical arrangements. We find that for certain specific geometries, such as an octupolarlike molecule with donors and acceptors of varying strengths at the branches, the hyperpolarizability is near the fundamental limit. In these cases, the molecule is observed to be well approximated by a three-level model, consistent with the three-level ansatz previously used to calculate the fundamental limits. However, when the hyperpolarizability is below the apparent limit (about a factor of 30 below the fundamental limit), the system is no longer representable by a three-level model, where both two-level and many-state models are found to be appropriate, depending on the symmetry.
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42.65.An Optical susceptibility, hyperpolarizability
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

Infrared absorption of CH3SO2 detected with time-resolved Fourier-transform spectroscopy

Li-Kang Chu and Yuan-Pern Lee

J. Chem. Phys. 124, 244301 (2006); http://dx.doi.org/10.1063/1.2211610 (8 pages) | Cited 14 times

Online Publication Date: 23 June 2006

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A step-scan Fourier-transform spectrometer coupled with a 6.4 m multipass absorption cell was employed to detect time-resolved infrared absorption spectra of the reaction intermediate CH3SO2 radical, produced upon irradiation of a flowing gaseous mixture of CH3I and SO2 in CO2 at 248 nm. Two transient bands with origins at 1280 and 1076 cm−1 were observed and are assigned to the SO2-antisymmetric and SO2-symmetric stretching modes of CH3SO2, respectively. Calculations with density-functional theory (B3LYP/aug-cc-pVTZ and B3P86/aug-cc-pVTZ) predicted the geometry, vibrational, and rotational parameters of CH3SO2 and CH3OSO. Based on predicted rotational parameters, the simulated absorption band of the SO2-antisymmetric stretching mode that is dominated by the b-type rotational structure agrees satisfactorily with experimental results. In addition, a band near 1159 cm−1 observed at a later period is tentatively attributed to CH3SO2I. The reaction kinetics of CH3+SO2→CH3SO2 and CH3SO2+I→CH3SO2I based on the rise and decay of absorption bands of CH3SO2 and CH3SO2I agree satisfactorily with previous reports.
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82.80.Dx Analytical methods involving electronic spectroscopy
82.20.Hf Product distribution
82.20.Db Transition state theory and statistical theories of rate constants
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions

Rotationally resolved S1←S0 electronic spectra of fluorene, carbazole, and dibenzofuran: Evidence for Herzberg-Teller coupling with the S2 state

John T. Yi, Leonardo Alvarez-Valtierra, and David W. Pratt

J. Chem. Phys. 124, 244302 (2006); http://dx.doi.org/10.1063/1.2206782 (7 pages) | Cited 4 times

Online Publication Date: 23 June 2006

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Rotationally resolved fluorescence excitation spectra of the S1←S0 origin bands and higher vibronic bands of fluorene (FLU), carbazole (CAR), and dibenzofuran (DBF) have been observed and assigned. Analyses of these data show that replacement of the CH2 group in FLU with a NH group in CAR and an O atom in DBF produces only localized changes in structure, in the ground state. But the three molecules exhibit different changes in geometry when they are excited by light. The S1 states of the three molecules also are electronically very different. The S1←S0 transition moments of CAR and DBF are parallel to the C2 symmetry axis whereas the corresponding transition moment in FLU is perpendicular to this axis. Herzberg-Teller coupling involving the S2 state also has been observed in the spectra of higher vibronic bands of CAR and DBF. Possible reasons for these behaviors are discussed.
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33.50.Dq Fluorescence and phosphorescence spectra
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors

Vibrational predissociation of H5+

Vladimír Špirko, Takayoshi Amano, and Wolfgang P. Kraemer

J. Chem. Phys. 124, 244303 (2006); http://dx.doi.org/10.1063/1.2207612 (5 pages) | Cited 3 times

Online Publication Date: 23 June 2006

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The full nine-dimensional vibrational Hamiltonian for H5+ described in the literature [ Kraemer et al., J. Mol. Spectrosc. 164, 500 (1994) ] is adopted here for an approximate evaluation of the spectral linewidths of the observed H–H stretching modes of the H5+ ion and the corresponding modes of its D5+ isotopomer. In this approximation the high dimensionality of the original Hamiltonian is reduced to a three-dimensional model Hamiltonian which takes only the H–H stretching modes and the molecular dissociation mode into consideration assuming that they are adiabatically separable from the remaining modes. To make the calculations numerically feasible, the molecular degenerate (“skeletal”) vibrations are assumed to take place in harmonic potentials, and the effect of the internal propeller rotation is completely disregarded. The linewidths calculated in this approximation are too small to explain the broad shapes of the observed spectral transitions. It can thus be argued that the failure to resolve rotational structure in the observed bands is mainly due to spectral congestion and only partly due to predissociation of the H5+ cluster.
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36.40.Mr Spectroscopy and geometrical structure of clusters
36.40.Wa Charged clusters
33.80.Gj Diffuse spectra; predissociation, photodissociation
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.70.Jg Line and band widths, shapes, and shifts

Nuclear electric quadrupole moments of Rb from the hyperfine spectrum of RbF

J. Cederberg, E. Frodermann, H. Tollerud, K. Huber, M. Bongard, J. Randolph, and D. Nitz

J. Chem. Phys. 124, 244304 (2006); http://dx.doi.org/10.1063/1.2212414 (3 pages) | Cited 6 times

Online Publication Date: 27 June 2006

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The molecular beam electric resonance technique has been used to examine the hyperfine spectrum of RbF. The Rb nuclear electric quadrupole interaction, the spin-rotation interactions, and tensor and scalar spin-spin interactions have been measured for both Rb isotopes, including their dependence on vibrational and rotational states. Transition frequencies have been determined to a precision of better than 1 Hz in many cases. The magnetic interactions in the two isotopomers are consistent with what is expected from the known masses and magnetic dipole moments. In the case of the Rb nuclear electric quadrupole interaction, adjustments have been made for a small isotopomer shift, and for the ratio of the effective nuclear electric quadrupole moments, Q(math)/Q(math) = 0.483 830 1±0.000 001 8. The effective quadrupole interaction includes a pseudoquadrupole interaction that may be significant at this level of precision, but cannot be distinguished experimentally.
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31.30.Gs Hyperfine interactions and isotope effects
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.15.Pw Fine and hyperfine structure
33.20.Sn Rotational analysis
33.20.Tp Vibrational analysis

Hyperfine spectrum of RbCl

J. Cederberg, S. Fortman, B. Porter, M. Etten, M. Feig, M. Bongard, and L. Langer

J. Chem. Phys. 124, 244305 (2006); http://dx.doi.org/10.1063/1.2212413 (3 pages) | Cited 4 times

Online Publication Date: 27 June 2006

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The molecular beam electric resonance technique has been used to conduct a high precision examination of the hyperfine spectrum of the four isotopomers of RbCl. Coupling constants for the nuclear electric quadrupole interactions, the spin-rotation interactions, the tensor and scalar spin-spin interactions, and a rubidium nuclear octupole interaction, and their dependence on vibrational and rotational states have been determined. The dominant interaction, the rubidium nuclear electric quadrupole interaction, shows a small shift with substitution of the chlorine isotope.
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31.30.Gs Hyperfine interactions and isotope effects
33.15.Pw Fine and hyperfine structure
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.70.Jg Line and band widths, shapes, and shifts
33.20.Sn Rotational analysis
33.20.Tp Vibrational analysis

State-to-state correlated study of CD3I photodissociation at 266 and 304 nm

Guosheng Li and Hyun Jin Hwang

J. Chem. Phys. 124, 244306 (2006); http://dx.doi.org/10.1063/1.2212938 (8 pages) | Cited 13 times

Online Publication Date: 28 June 2006

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High-resolution photofragment translational spectroscopy is used in this work to measure the translational and internal energy distributions in the CD3 and iodine fragments produced from the photodissociation of CD3I at 266 and 304 nm. Channel selected detection, via resonantly enhanced multiphoton ionization, combined with one-dimensional core sampling provides detailed information about vibrational state distributions of the CD3 fragments. The vibrational state distributions of CD3 fragments in the I*(math) channel have a propensity of ν2′ umbrella bending mode with a maximum at ν2′ = 1 for 266 nm photodissociation. For I*(math) channel at 304 nm photodissociation, vibrational state distributions of CD3 fragment have a maximum in the vibrational ground state. For the I(math) channel (math←math), ν2′ umbrella bending vibrational distribution is measured as the predominant vibrational mode but has a much broader distribution when compared to that of the I* channel. The vibrational state distributions of the CD3 fragment produced from the perpendicular transition, i.e., math, which was determined at 304 nm photodissociation, has a maximum at ν2′ = 1. The curve crossing possibility between the math and math adiabatic potentials is determined as 0.19 for 266 and 0.85 for 304 nm. The trend in reaction dynamics in 266 and 304 nm photodissociation of CD3I is compared with theoretical calculations. A bond dissociation energy D0(C–I) = 56.60±0.5 kcal/mol was derived by applying laws of energy conservation.
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33.80.Gj Diffuse spectra; predissociation, photodissociation
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
33.80.Eh Autoionization, photoionization, and photodetachment
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Tp Vibrational analysis
33.15.Fm Bond strengths, dissociation energies

Semiclassical nonadiabatic dynamics based on quantum trajectories for the O(math,math)+H2 system

Sophya Garashchuk, Vitaly A. Rassolov, and George C. Schatz

J. Chem. Phys. 124, 244307 (2006); http://dx.doi.org/10.1063/1.2208615 (8 pages) | Cited 9 times

Online Publication Date: 28 June 2006

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The O(math,math)+H2→OH+H reaction is studied using trajectory dynamics within the approximate quantum potential approach. Calculations of the wave-packet reaction probabilities are performed for four coupled electronic states for total angular momentum J = 0 using a mixed coordinate/polar representation of the wave function. Semiclassical dynamics is based on a single set of trajectories evolving on an effective potential-energy surface and in the presence of the approximate quantum potential. Population functions associated with each trajectory are computed for each electronic state. The effective surface is a linear combination of the electronic states with the contributions of individual components defined by their time-dependent average populations. The wave-packet reaction probabilities are in good agreement with the quantum-mechanical results. Intersystem crossing is found to have negligible effect on reaction probabilities summed over final electronic states.
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82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.20.Fd Collision theories; trajectory models
82.20.Ln Semiclassical theory of reactions and/or energy transfer
82.20.Kh Potential energy surfaces for chemical reactions

Experimental structure determination of silver cluster ions (Agn+,19 ⩽ n ⩽ 79)

Martine N. Blom, Detlef Schooss, Jason Stairs, and Manfred M. Kappes

J. Chem. Phys. 124, 244308 (2006); http://dx.doi.org/10.1063/1.2208610 (10 pages) | Cited 13 times

Online Publication Date: 28 June 2006

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The structures of mass selected silver cluster cations Ag19+, Ag38+, Ag55+, Ag59+, Ag75+, and Ag79+ have been probed at a temperature of 100 K by trapped ion electron diffraction. The structure assignment is carried out by comparison of the experimental scattering intensity with theoretical scattering functions of calculated candidate structures obtained by density functional theory. For the cluster sizes studied the resulting experimental data are invariably best described by structures based on the icosahedral motif, while closed packed structures can be ruled out.
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61.46.Bc Structure of clusters (e.g., metcars; not fragments of crystals; free or loosely aggregated or loosely attached to a substrate)

Isotopic and internal CX3 (X = D,H) rotational motion effects in the Ba⋯FCX3+hν→BaF+CX3 intracluster reactions

C. A. Rinaldi, K. Gasmi, S. Skowronek, and A. González Ureña

J. Chem. Phys. 124, 244309 (2006); http://dx.doi.org/10.1063/1.2208618 (5 pages) | Cited 1 time

Online Publication Date: 28 June 2006

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Photodepletion and action spectra of the laser-induced Ba⋯FCD3 fragmentation have been measured over the 16 075–16 380 cm−1 range. The observed band and peak structures allowed us to estimate the vibrational and rotational structures of the excited complex at the transition state configuration. The relative reaction probability PR(E) for the intracluster Ba⋯FCD3+hν→BaF+CD3 reaction has been determined over the cited energy range. PR(E) shows a peak structure with an energy spacing of 8.9 cm−1 which was attributed to an internal rotation of the CD3 group in the intermediate state. A comparison with previous Ba⋯FCH3 photofragmentation spectra reveals the dynamical role of the internal CX3 (X = H,D) motion which is manifested by the presence of rotational resonances in the laser-induced intracluster reaction.
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82.20.Tr Kinetic isotope effects including muonium
82.20.Db Transition state theory and statistical theories of rate constants
82.20.Kh Potential energy surfaces for chemical reactions
82.50.-m Photochemistry

Identifying reactive trajectories using a moving transition state

Thomas Bartsch, T. Uzer, Jeremy M. Moix, and Rigoberto Hernandez

J. Chem. Phys. 124, 244310 (2006); http://dx.doi.org/10.1063/1.2206587 (13 pages) | Cited 16 times

Online Publication Date: 28 June 2006

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A time-dependent no-recrossing dividing surface is shown to lead to a new criterion for identifying reactive trajectories well before they are evolved to infinite time. Numerical dynamics simulations of a dissipative anharmonic two-dimensional system confirm the efficiency of this approach. The results are compared to the standard fixed transition state dividing surface that is well-known to suffer from recrossings and therefore requires trajectories to be evolved over a long time interval before they can reliably be classified as reactive or nonreactive. The moving dividing surface can be used to identify reactive trajectories in harmonic or moderately anharmonic systems with considerably lower numerical effort or even without any simulation at all.
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82.20.Db Transition state theory and statistical theories of rate constants

Quantum state tomography of molecular rotation

Anders S. Mouritzen and Klaus Mølmer

J. Chem. Phys. 124, 244311 (2006); http://dx.doi.org/10.1063/1.2208351 (7 pages) | Cited 11 times

Online Publication Date: 28 June 2006

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We show how the rotational quantum state of a linear or symmetric top rotor can be reconstructed from finite time observations of the polar angular distribution under certain conditions. The presented tomographic method can reconstruct the complete rotational quantum state in many nonadiabatic alignment experiments. Our analysis applies for measurement data available in principle with existing measurement techniques. In practice, a full reconstruction requires a large amount of data and is thus experimentally challenging. Nonetheless, showing that the necessary information is present, we substantiate the use of approximate reconstruction methods with such data.
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31.15.-p Calculations and mathematical techniques in atomic and molecular physics
33.15.Bh General molecular conformation and symmetry; stereochemistry
33.15.Mt Rotation, vibration, and vibration-rotation constants

Experimental and theoretical investigation of the Raman and hyper-Raman spectra of acetonitrile and its derivatives

Olivier Quinet, Benoît Champagne, and Vincent Rodriguez

J. Chem. Phys. 124, 244312 (2006); http://dx.doi.org/10.1063/1.2208350 (12 pages) | Cited 13 times

Online Publication Date: 28 June 2006

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The Raman and hyper-Raman spectra of acetonitrile and its deuterated analog have been investigated by combining experimental analysis and theoretical interpretation. It has been observed that the Raman spectra can easily be reproduced at both the Hartree-Fock and Møller-Plesset second-order levels of approximation and that for these fundamental transitions, inclusion of anharmonicity effects is not essential. On the other hand, the hyper-Raman spectra are more difficult to simulate and interpret. In particular, electron correlation has to be included in order to describe properly the intensity of the CN stretching mode. Then, a pseudo-C∞v symmetry was assumed to better fit the experimental observations. This accounts for the fact that the a1- and e-symmetry modes correspond to time-decoupled vibrations. The e-symmetry modes, associated with nuclear motions perpendicular to the molecular axis are indeed subject to relaxation processes and, except the CCN bending mode, not visible in the hyper-Raman spectra of acetonitrile or of its deuterated analog. This assumption is supported by the gradual decrease of the phenomenon when going from acetonitrile to trichloroacetonitrile, where the presence of the heavier chlorine atoms in the latter reduces the relaxation processes.
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33.20.Fb Raman and Rayleigh spectra (including optical scattering)
31.15.xp Perturbation theory
31.15.xr Self-consistent-field methods
33.20.Tp Vibrational analysis
back to top Condensed Phase Dynamics, Structure, and Thermodynamics: Spectroscopy, Reactions, and Relaxation

Prediction among different spectroscopic properties for aqueous systems

Xiao Zhu, Jia Yao, Haoran Li, and Shijun Han

J. Chem. Phys. 124, 244501 (2006); http://dx.doi.org/10.1063/1.2206769 (5 pages) | Cited 1 time

Online Publication Date: 23 June 2006

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Spectroscopic properties obtained by NMR and vibrational spectra both reflect the microscopic environment of solutions, and the local composition (LC) theory can be used to study environmental effects on spectroscopic properties. Based on the LC model, the relationship between NMR and vibrational spectra, including infrared (IR) spectroscopy and Raman, were investigated. For the aqueous systems—water+N, N-dimethylformamide, water+acetone, water+methanol, and water+ethanol, we performed prediction between concentration-dependent peak positions of IR and Raman, as well as between concentration-dependent vibrational properties and math NMR chemical shifts. The results showed that reliable prediction could be achieved with the help of the LC model. This suggests that math NMR chemical shifts and vibrational spectroscopic properties may tell us the same story about the local environment encountered in solution.
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76.60.Cq Chemical and Knight shifts
78.30.C- Liquids
61.20.Gy Theory and models of liquid structure

The methyl C–H blueshift in N,N-dimethylformamide-water mixtures probed by two-dimensional Fourier-transform infrared spectroscopy

Zheng Xu, Haoran Li, Congmin Wang, Haihua Pan, and Shijun Han

J. Chem. Phys. 124, 244502 (2006); http://dx.doi.org/10.1063/1.2206177 (10 pages) | Cited 11 times

Online Publication Date: 26 June 2006

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Two-dimensional correlation spectroscopy was used to study the composition-dependent spectral variations of the CH-stretching bands of N,N-dimethylformamide (DMF)-water mixtures with XDMF ranging from 0.98 to 0.60. By a detailed correlation analysis of the spectral changes of the CH- and OH-stretching bands, it is found that the intensities of the CH and OH bands change in different ways when the water content is increased. It is also found that two different regions of the water content can be distinguished, in which the intensity changes have different signatures. A tentative explanation for how these phenomena might be related to structural changes in the mixture is proposed. The structural change of DMF induced by the water hydrogen bonded on the carbonyl group is supposed to be the possible origin of the methyl C–H blueshift instead of the direct C–H⋯O interactions before the hydrophobic hydration takes place.
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78.30.C- Liquids
63.50.-x Vibrational states in disordered systems
61.25.Em Molecular liquids

Coherent spectroscopy in dissipative media: Time-domain studies of channel phase and signal interferometry

S. Ramakrishna and Tamar Seideman

J. Chem. Phys. 124, 244503 (2006); http://dx.doi.org/10.1063/1.2209234 (8 pages)

Online Publication Date: 27 June 2006

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We extend a recently formulated coherence spectroscopy of dissipative media [ J. Chem. Phys. 122, 084502 (2005) ] from the stationary excitation limit to the time domain. Our results are based on analytical and numerical solutions of the quantum Liouville equation within the Bloch framework. It is shown that the short pulse introduces a new, controllable time scale that allows better insight into the relation between the coherence signal and the phase properties of the material system. We point to the relation between the time-domain coherence spectroscopy and the method of interferometric two-photon photoemission spectroscopy, and propose a variant of the latter method, where the two time-delayed excitation pathways are distinguishable, rather than identical. In particular, we show that distinguishability of the two excitation pathways introduces the new possibility of disentangling decoherence from population relaxation.
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79.60.-i Photoemission and photoelectron spectra
02.30.Rz Integral equations
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