Biomedical subjects

A A Buchachenko

Publications and source records attributed to A A Buchachenko.

6 recordsLinked to original sources

PubMed2006

Ab initio potential energy surface, infrared spectra, and dynamics of the ion-molecule complexes between Br- and H2, D2, and HD.

A three-dimensional potential energy surface (PES) for the Br(-)-H(2) complex is computed using the ab initio CCSD(T) method and an extended basis set. The PES has two equivalent minima at the linear geometries (equilibrium interfragment distance R(e)=3.34 A and interaction energy D(e)=670 cm(-1)) separated by the barrier at the T-shaped configuration (interfragment distance R(e)=4.03 A and barrier height of 610 cm(-1)). Ab initio points are fitted to a flexible analytical form and used in the variational rovibrational energy level calculations. Simulated infrared spectra of the Br(-)-H(2) and Br(-)-D(2) complexes in the monomer stretching excitation region are in good agreement with the measured ones. Nonstatistical intensity ratios of the complexes of para- and ortho-monomers are qualitatively explained by monomer ligand exchange reactions. Predissociation of the complexes containing vibrationally excited monomers is analyzed and shown to proceed through the near-resonant vibration-to-rotation energy transfer. For complexes involving Br(-) and the HD monomer, two energetically low-lying states are predicted, corresponding predominately to the Br(-)-DH and Br(-)-HD isomeric forms. The results demonstrate the close similarity of the bromide containing complexes to their analogs containing the chloride anion.

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PubMed2005

Electronic interaction anisotropy between open-shell lanthanide atoms and helium from cold collision experiment.

Based on measurements of the Zeeman relaxation in a cold gas of (3)He [C. I. Hancox, S. C. Doret, M. I. Hummon, L. Luo, and J. M. Doyle, Nature (London) 431, 281 (2004)], we show that the electronic interaction anisotropy between rare-earth atoms with nonzero electronic orbital angular momenta and helium is extremely small. The interaction of the rare-earth atoms with He gives rise to several adiabatic potentials with different electronic symmetries. It is demonstrated that the energy splitting between these potentials does not exceed 0.09 cm(-1) at interatomic distances larger than the turning point for collisions at 0.8 K, including the region of the van der Waals interaction minima.

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PubMed2005

Collision-induced nonadiabatic transitions in the second-tier ion-pair states of iodine molecule: experimental and theoretical study of the I2(f0g+) collisions with rare gas atoms.

Nonadiabatic transitions induced by collisions with He, Ar, Kr, and Xe atoms in the I(2) molecule excited to the f0(g)(+) second-tier ion-pair state are investigated by means of the optical-optical double resonance spectroscopy. Fluorescence spectra reveal that the transition to the F0(u)(+) state is a dominant nonradiative decay channel for f state in He, Ar, and Kr, whereas the reactive quenching is more efficient for collisions with Xe atom. Total rate constants and vibrational product state distributions for the f-->F electronic energy transfer are determined and analyzed in terms of energy gaps and Franck-Condon factors for the combining vibronic levels at initial vibrational excitations v(f)=8, 10, 14, and 17. Quantum scattering calculations are performed for collisions with He and Ar atoms, implementing a combination of the diatomics-in-molecule and long-range perturbation theories to evaluate diabatic PESs and coupling matrix elements. Calculated rate constants and vibrational product state distributions agree well with the measured ones, especially in case of Ar. Qualitative comparison is made with the previous results for the second-tier f0(g)(+)-->F0(u)(+) transition in collisions with I(2)(X) molecule and the first-tier E0(g)(+)-->D0(u)(+) transition induced by collisions with the rare gas atoms.

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PubMed2005

Interaction potentials of the RG-I anions, neutrals, and cations (RG = He, Ne, Ar).

Interaction potentials of the iodine atom, atomic cation, and anion with light rare-gas atoms from He to Ar are calculated within the unified ab initio approach using the unrestricted coupled-cluster with singles and doubles and perturbative treatment of triples correlation treatment, relativistic small-core pseudopotential, and an extended basis set. Ab initio points are fit to a flexible analytical function. The calculated potentials are compared with available literature data, assessed in the I(-)-and I+-ion mobility calculations and the Ar-I(-)-anion zero electron kinetic-energy spectra simulations, and analyzed using the correlation rules. The results indicate a high precision of the reported potentials.

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PubMed2004

Isomeric interconversion in the linear Cl(-)-HD anion complex.

The rotationally resolved infrared photodissociation spectrum of Cl(-)-HD is measured in the HD stretch region. Two Sigma-Sigma bands are observed, corresponding to transitions from the ground state [the (nuHD = 0, n = 0) level] and first excited intermolecular bend state [the (nuHD = 0, n = 1) level]. The (nuHD = 0, n = 0) and (nuHD = 0, n = 1) states are predominantly associated with the linear Cl-...DH and Cl-...HD geometries, respectively. The spectrum is complicated by perturbative interactions between levels of the (nuHD = 0, n = 0) and (nuHD = 0, n = 1) rotational manifolds and between levels of the (nuHD = 1, n = 0) and (nuHD = 1, n = 1) rotational manifolds. A global fit to the transition frequencies, taking the lower and upper state perturbations into account, yields zero-order rotational and centrifugal distortion constants and allows us to establish that the (nuHD = 0, n = 1, J" = 0) level lies 13.7 cm(-1) above the (nuHD = 0, n = 0, J" = 0) level. Rovibrational energy level calculations performed using a recent ab initio potential energy surface confirm the picture emerging from the experimental data and provide good agreement with measured molecular parameters. The results emphasize the importance of quantum mechanical interconversion between two isomeric structures of a simple anion complex.

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PubMed2004

The open-shell interaction of He with the B 3Piu(0+) state of Br2: an ab initio study and its comparison with a diatomics-in-molecule perturbation model.

The interaction of He with Br2 in electronically excited B 3Piu state is investigated using spin-unrestricted single and double coupled-cluster approach with noniterative perturbative treatment of triple excitations. Internal electrons of the Br atom are described by effective core pseudopotentials. The validity of this approach is analyzed by comparing the lowest 2Sigma+ and 2Pi electronic states of the HeBr molecule with those obtained in all electron calculations [J. Chem. Phys. 115, 10438 (2001)]. In this context, we examine the performance of different basis sets and saturation with bond functions. The comparison of theoretical blue-shifts with the experiment provides confidence about the present ab initio calculations. In addition, He-Br results of ab initio calculations at the same level are used to obtain approximate He-Br2 (3Piu) interactions in the framework of the diatomics-in-molecule first order perturbation theory (IDIM-PT1) [J. Chem. Phys. 104, 9913 (1996)]. Overall, the IDIM-PT1 model results show a good agreement with the ab initio ones, being the main difference the sensitivity to the elongation of the Br-Br bond.

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