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The authors report adaptive resolution molecular dynamics simulations of a flexible linear polymer in solution. The solvent, i.e., a liquid of tetrahedral molecules, is represented within a certain radius from the polymer’s center of mass with a high level of detail, while a lower coarse-grained resolution is used for the more distant solvent. The high resolution sphere moves with the polymer and freely exchanges molecules with the low resolution region through a transition regime. The solvent molecules change their resolution and number of degrees of freedom on the fly. The authors show that their approach correctly reproduces the static and dynamic properties of the polymer chain and surrounding solvent. [ABSTRACT FROM AUTHOR]

Time-resolved coherent anti-Stokes Raman-scattering (CARS) measurements are carried out to study the interaction between xenon atom and iodine molecule in a solid krypton matrix. Interference between the CARS polarizations of the “free” and complexed iodine molecules is observed, while the quantum beats of the complex are not detected due to low concentration. Vibrational analysis based on the polarization beats yields accurate molecular constants for the I2–Xe complex. The harmonic frequency of the I2–Xe complex is found to be redshifted by 0.90 cm-1 when compared to the free I2, whereas the anharmonicity is approximately the same. The dephasing rate of the complex is found to be somewhat higher than that of the free iodine molecule in solid Kr, showing that the complexation affects dephasing, although not dramatically. Molecular dynamics simulations are carried out to find the conformation of the complex, and wave packet simulations are used to reproduce the CARS signal to confirm the assignments of the observed beatings as quantum and polarization beats. The results show that the polarization beats are a useful tool for investigating weak interactions in condensed phase. [ABSTRACT FROM AUTHOR]

The hindered rotational states of molecules confined in crystal fields of octahedral symmetry, and their time-dependent alignment obtained by pulsed nonresonant laser fields, are studied computationally. The control over the molecular axis direction is discussed based on the evolution of the rotational wave packet generated in the cubic crystal-field potential. The alignment degree obtained in a cooperative case, where the alignment field is applied in a favorable crystal-field direction, or in a competitive direction, where the crystal field has a saddle point, is presented. The investigation is divided into two time regimes where the pulse duration is either ultrashort, leading to nonadiabatic dynamics, or long with respect to period of molecular libration, which leads to synchronous alignment due to nearly adiabatic following. The results are contrasted to existing gas phase studies. In particular, the irregularity of the crystal-field energies leads to persistent interference patterns in the alignment signals. The use of nonadiabatic alignment for interrogation of crystal-field energetics and the use of adiabatic alignment for directional control of molecular dynamics in solids are proposed as practical applications. [ABSTRACT FROM AUTHOR]

Reports on ab initio and molecular dynamics studies on rare gas hydrides. Potential energy curves; Isotropic hyperfine properties; Matrix cage trapping of atomic hydrogen; Derivation of classical trajectories for nuclear motion in a lattice with a single hydrogen atom.

The anisotropic boron atom electron paramagnetic resonance spectra measured in rare gas matrices (Ar, Kr, Xe) are interpreted with the aid of highly correlated ab initio calculations including spin-orbit coupling and diatomics-in-molecules (DIM) molecular dynamics simulations. The heavy-element and crystal field effects are inspected as they contribute to the electron g-shift. The DIM-simulated p-orbital splittings and lattice perturbed hyperfine coupling values provide a good starting point for spectral fitting and show the correctness of the guidelines given by purely synthetic generation of the spectra. The present combination of experiment and theory resulted in improved accuracy of the parameters measured in Ar matrix, new values are extracted for Kr matrix, and tentative assignment is also provided for the Xe matrix case. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The absorption spectrum of I2in solid Xe shows resolvedzero-phonon lines and phonon side bands near the origin of the B←Xtransition (550–625 nm). The long-lived |B⟩⟨X| coherence in this energy range(T2= 600 fs on average) emerges as vibrationallyunrelaxed fluorescence in resonance Raman (RR) spectra. Upon excitationin the structureless continuum at 532 nm, the oscillatory RR progressionexhibits electronic dephasing time of T2= 150 fs. Two RR progressions with markedly different vibrationalcoherence on the X-state are observed. The main progression of sharpovertones (T2> 21 ps) is assignedtomolecules trapped in double-substitution sites. The minor progression,which shows dephasing times T2= 6–0.6ps for v= 1–8, is assigned to molecules intriple-substitution sites. The line progressions allow a detailedcharacterization of the solvated B- and X-state potentials. Time-resolvedcoherent anti-Stokes Raman scattering is used to probe selected vibrationalcoherences on the X-state. Assignments are obtained through moleculardynamics simulations, which reproduce the relative dephasing ratesbetween the two sites, clarify the role of rotation-translation dynamics,and enable quantum dynamics simulations of the spectra by the potentialsof mean force that accurately describe the molecule–surroundinginteractions. [ABSTRACT FROM AUTHOR]