Positron annihilation on many molecules occurs via positron capture into vibrational Feshbach resonances, with annihilation rates often further enhanced by energy transfer to vibrational excitations weakly coupled to the positron continuum. Data presented here uncover another scenario in which the positron couples directly to a quasicontinuum of multimode vibrational states. A model that assume...

Ecol = energy of collision, eV j, j 0 = initial and final rotational quantum numbers K = bound–bound transition rate, cm∕s ni = number density of O2 rovibrational level i, cm−3 nO = number density of atomic oxygen, cm−3 T, Tvib = translational, vibrational, and rotational temperatures, K v, v 0 = initial and final vibrational quantum numbers σ = cross section, Å τvib, τrot = vibrational and rot...

We have calculated free energy and vibrational entropy differences in Ni3Al between its equilibrium ordered structure and a disordered fcc solid solution. The free energy and entropy differences were calculated using the method of adiabatic switching in a molecular-dynamics formalism. The path chosen for the free-energy calculations directly connects the disordered with the ordered state. The a...

Pentaerythritol tetranitrate (PETN) is a common secondary explosive and has been used extensively to study shock initiation and energy propagation in energetic materials. We report 2D IR measurements of PETN thin films that resolve vibrational energy transfer and relaxation mechanisms. Ultrafast anisotropy measurements reveal a sub-500 fs reorientation of transition dipoles in thin films of vap...

The methodology for a vibrational analysis within the nuclear–electronic orbital ~NEO! framework is presented. In the NEO approach, specified nuclei are treated quantum mechanically on the same level as the electrons, and mixed nuclear–electronic wave functions are calculated variationally with molecular orbital methods. Both electronic and nuclear molecular orbitals are expressed as linear com...

in order to represent the potential energy function over the whole range of r, many potentialenergy functions have been proposed. in the present paper, we employ many potential energyfunctions, to use numerov method for solving the nuclear schrödinger equation for the ifmolecule, as an example of a heteronuclear diatomic molecules. then we determine thespectroscopic constants eω , e e x ω , e b...

Solitons arise as static solutions of finite energy to the equations of motion of non linear field theories. A given solution in general depends upon a set of parameters or moduli, and is a point in the manifold of solutions of equal energy, or moduli space. In many cases this manifold is simply a coset space G/H where G is the group of symmetries of the action and H ⊂ G is the symmetry of the ...

A thorough conformational analysis of ibuprofen [2-(4-isobutylphenyl) propionic acid] was carried by out, using density functional theory (DFT) calculations coupled to optical vibrational spectroscopy (both Raman and FTIR). Eight different geometries were found to be energy minima. The relative orientations of the substituent groups in the ibuprofen molecule, which can be considered as a para-s...

Nuclear vibrations play a prominent role in the spectroscopy and dynamics of electronic systems. As recent experimental and theoretical studies suggest, this may be even more so when vibrational frequencies are resonant with transitions between the electronic states. Herein, a vibronic multilevel Redfield model is reported for excitonically coupled electronic two-level systems with a few explic...

1 By following the scheme of the Grid Empowered Molecular Simulator (GEMS) a 2 new O2 + N2 intermolecular potential, built on ab initio calculations and experimental 3 (scattering and second virial coe cient) data, has been coupled with an appropriate 4 intramolecular one. On the resulting potential energy surface detailed rate coe cients 5 for collision induced vibrational energy exchanges hav...