Junko Takahashi

Meiji Gakuin University · Faculty of Law

Photodesorption of CO ice is suggested to be the main process that maintains a measureable amount of gaseous CO in cold interstellar clouds. A classical molecular dynamics simulation is used to gain insight into the underlying mechanism. Site-site pair potentials were developed based on ab initio calculations for the ground and excited non-rigid CO...

The Molecular Dynamics (MD) method was employed to model hydrogen molecules interacting on the surface of amorphous ice and the sticking coefficients of H2 were calculated. Interstellar dust grains are mostly composed of carbon or silicate grains with layers of amorphous ice on their surface. Interaction of molecular hydrogen with these grain surfa...

A classical Molecular Dynamics (MD) method is employed to model hydrogen molecules interacting with the surface of amorphous ice and to calculate the sticking coefficient as a function of various system parameters. This study, combining molecular physics and surface science, is part of a larger program of research to provide theoretical input for m...

The formation pumping mechanism of H2 molecules formed on icy mantles of interstellar dust was investigated theoretically based on a classical molecular dynamics (MD) computational simulation. The slab-shaped amorphous water ice was prepared at 10 and 70 K, as a realistic model surface for icy mantles of dust, and the formation process of molecular...

This paper considers experimental and theoretical studies of the H2 formation process on solid surfaces in an attempt to determine the ortho/para ratio (OPR) of H2 newly formed on dust grains. Estimates of OPRs and formation temperatures of H2 on icy mantles, silicate dust, and carbonaceous dust are given based on a new model. The OPR of H2 newly f...

It has been predicted that H2 newly formed on the surface of dust grains should be in highly vibrationally and rotationally excited states in the ground electronic state via the formation pumping mechanism. This suggests that the rovibrational emission spectrum of H2 may be detectable even in regions without a source of UV pumping or dynamical exci...

Formation of H2 in interstellar gas occurs primarily via surface reactions on grains. A key parameter in determining the efficiency of H2 formation is the probability for H to stick to the surface. Once H2 is formed it may return to the surface and participate in further reactive processes. However, little is known about the sticking probability of...

It has been predicted that H2 newly formed on the surface of dust grains should be in highly vibrationally and rotationally excited states in the ground electronic state via the formation pumping mechanism. This suggests that the rovibrational emission spectrum of H2 may be detectable even in regions without a source of ultraviolet (UV) pumping or...

The chemical desorption of an adsorbed CO molecule in the vicinity of H2-forming sites on cosmic dust grains in cold dense clouds is investigated theoretically, mainly using a model based on a classical molecular dynamics computational simulation. As a model surface for icy mantles of dust grains, an amorphous water ice slab is generated at 10 K, a...

It has been predicted that H2 newly formed on the surface of dust grains should be in highly vibrationally and rotationally excited states in the ground electronic state via the formation pumping mechanism. This suggests that rovibrational H2 emission may be detectable even in regions without a source of ultraviolet (UV) pumping or dynamical excita...

Classical molecular dynamics (MD) computer simulations were performed to investigate the whole fundamental processes of the H 2 formation reaction on the amorphous water ice as a model surface of icy mantles of dust grains. The product energy distribution and formation pumping mechanism of H 2 for med on dust grains were also examined.

Detectable new isomers of interstellar carbon-chain (linear) radicals, Cn(n=2–8), were investigated theoretically based on ab initio quantum chemical calculations. The molecular characteristics of various Cn(n=3–8) isomers were examined, and it was found that 3-ring isomers (isomers with a three-member-carbon-ring) of C3H, C5H, and C7H are at a low...

Recent advances in theoretical simulations of grain-surface processes are reviewed. Classical molecular dynamics (MD) computer simulations were performed to investigate the whole process of H 2 formation on icy mantles of interstellar dust grains within a single model. Amorphous water ice slabs were generated at 10 K and 70 K as a realistic model s...

Recent advances in a series of studies based on the molecular dynamics (MD) computer simulation that was performed to investigate the whole of H 2 formation process on the surface of dust grains throughout within a single model are reviewed. Amorphous water ice slabs were generated at 10 K and 70 K as a model surface of dust grains, and then the fi...

Chemical desorption of an adsorbed CO molecule in the vicinity of H _2 forming sites on interstellar dust grains is investigated by a theoretical modelling based on a classical molecular dynamics (MD) computational simulation. As a model surface for icy mantles of dust grains, the amorphous water ice slab was generated at 10 K, and the first and th...

The fundamental processes of H2 formation via H + H → H2 on the surfaces of icy mantles of interstellar dust have been investigated consistently within a single model based on a classical molecular dynamics (MD) computational simulation. As a model surface for icy mantles of dust grains, an amorphous water ice slab was generated at 10 and 70 K unde...

The diffusion process of a hydrogen atom on the amorphous water ice surface was investigated under very low temperature conditions (10 and 70 K) using both classical and quantum approaches. The model amorphous water ice slab was prepared by the classical molecular dynamics (MD) simulation under the two-dimensional periodic boundary condition with 1...

The sticking and the diffusion processes of a hydrogen atom on the surface of icy mantle of dust grains have been investigated based on the classical molecular dynamics (MD) simulation. As the model for the icy mantle, a slab-shaped amorphous water ice with infinite area was generated by MD simulation under the periodic boundary condition. It was f...

In the present work, we investigate the sticking process of a hydrogen atom on the surface of dust grains. As a realistic model for the icy mantle of dust grains, we produced slab-shaped amorphous water ice with infinite area by classical molecular dynamics (MD) computational simulation using two-dimensional periodic boundary condition. The resulti...

Abinitio molecular orbital calculations have been performed on the interstellar molecules C3H2 and C3H, and the reaction pathway including them for the neutral–neutral reactions C(3P)+C2H2 in interstellar clouds were examined. The optimized structures, rotational constants, dipole moments, vibrational frequencies, IR intensities, and relative energ...

The effect of vibronic coupling on the absorption band at ca.400 nm as well as on the Raman spectrum of the phenoxy radical (The IUPAC nomenclature recommends phenoxyl. However, in spectroscopic studies most authors prefer phenoxy to phenoxyl.) is examined by ab initio MO calculations within the framework of the adiabatic approximation. The vibroni...

The electronic structures of the phenoxyl radical in the electronic ground and excited states are studied by ab initio MO calculations. The geometries are optimized by the CAS-MCSCF procedure with the Huzinaga-Dunning DZV basis set. The electronic excitation energies and transition dipole moments are calculated by the CI procedure. According to the...

The thermal rate constants for SiH4 reversible arrow SiH3+H and CH4 reversible arrow CH3+H are calculated by the Canonical Variational Transition State Theory (CVTST). The minimum energy path potential and the deformation path potential along the reaction coordinate are calculated by the MCSCF-CI and UHF methods, respectively. The transitional bend...