The temperature jump and slow evaporation in molecular gases

We set up model transport equations that describe the behavior of molecular (diatomic and polyatomic) gases with a molecule collision rate proportional to the molecular velocity. In deriving these equations we allow for the internal (rotational) degrees of freedom, while the vibrational degrees of freedom are assumed “frozen.” We also set up an exact equation for the problem of the temperature jump with allowance for slow evaporation from the liquid surface into the saturated vapor atmosphere. Finally, we derive explicit formulas for calculating the coefficients of the temperature jump and gas-density jump above a flat surface and do the necessary numerical calculations. Zh. éksp. Teor. Fiz. 114, 956–971 (September 1998)     

Quantum kinetic Boltzmann equation taking into account the resonant exchange of excitations

A derivation of the quantum Boltzmann equation is given for identical particles with internal degrees of freedom. It is shown that the off-diagonal (with respect to the internal degrees of freedom) term of the equation contains an energy pole term, which is not present in the most commonly used kinetic equation, known as the Waldmann-Snider equation. The physical conditions underlying the occurrence of the pole term in the quantum kinetic equation are analyzed. Zh. éksp. Teor. Fiz. 111, 831–837 (March 1997)     

Translational-rotational interaction in dynamics and thermodynamics of a two-dimensional atomic crystal with molecular impurities

The interaction between the rotational degrees of freedom of a diatomic impurity molecule and phonon excitations of a two-dimensional atomic matrix commensurate to the substrate is investigated theoretically. It is shown that the translational-rotational interaction leads to renormalization of the crystal field constants and a change in the form of the operator for the rotational kinetic energy as compared to the corresponding expression for a free rotator. The contribution from the rotational degrees of freedom of impurities to the low-temperature heat capacity of a diluted solution of diatomic molecules in the two-dimensional atomic matrix is calculated. The possibility of experimentally observing the predicted effects is discussed.     

Rovibrational excitation within the infinite conical well: Desorption of diatomic molecules

An analytic model for the hindered rotational states of a diatomic molecule adsorbed upright on a solid surface is discussed. Various model dynamics situations, within the sudden approximation, designed to simulate desorption are presented and rotational state distributions are calculated including both rotational and translational degrees of freedom. Criteria are established for observing rotationally cool desorbed molecules.     

Construction of the mass velocity profile for a rarefied molecular gas entrained by a rotating sphere taking into account thermophysical parameters of the gas

The problem of a sphere rotating in a molecular gas is solved in the isothermal approximation. The expression for the velocity of a rarefied molecular gas entrained by a sphere rotating in it is derived for sliding flow conditions taking into account the second-order correction in the Knudsen number. A generalization of the Boltzmann kinetic equation in the BGK model to the case of rotational degrees of freedom of gas molecules is used as the basic equation. The diffusive reflection model is employed as the microscopic boundary condition on the surface of the sphere. It is shown that this approach makes it possible to take into account the dependence of the gas velocity on the Prandtl number and gas temperature.     

Rarefied molecular gas flow near the rotating cylindrical surface

An exact analytic solution of the problem of the right circular cylinder in a rarefied molecular gas is constructed in the isothermal approximation. An expression for the velocity of a rarefied molecular gas entrained by the cylinder rotated therein is obtained in the regime of a flow with slip accounting for the second-order correction in terms of the Knudsen number. A generalization of the BGK model of the Boltzmann kinetic equation accounting for the rotational degrees of freedom of gas molecules is used as the governing equation, and the diffuse reflection model is used as a microscopic boundary condition on the cylinder surface. The given approach is shown to enable the consideration of the gas flow dependence on the Prandtl number and the gas temperature.     

Core level photoemission evidence of frustrated surface molecules: a germ of disorder at the (111) surface of C60 before the order-disorder surface phase transition

Using high resolution core level photoemission, we investigated the disordering transition of the fullerene molecules at the (111) surface of C (60) films. The experimental evidence of a two-step mechanism for the rotational disordering of surface fullerene molecules is provided. The data are consistent with a recent model in which the rotational degrees of freedom of one molecule, out of the four inequivalent C (60) molecules of the low temperature (2x2) surface unit cell, melt about 100 K before the bulk phase transition.     

Laboratory Microwave Spectroscopy of Interstellar Molecules

Abstract

Modern radio astronomy has revealed that various kinds of molecules exist in ther very cold region between stars: interstellar space. An electromagnetic wave with a wavelength of a few centimeters to 1 mm corresponds in energy to a few to ten degrees of Kelvin. A molecule having its spectrum in this energy region provides us with valuable information about the low-energy environment where the molecule exists. New information provided by radio astronomy has rarely been     

Photoprocesses on a surface of nanoporous quartz under resonant laser radiation

The photoexcitation of iodine molecules on surfaces of solid (nonporous) and nanoporous quartz by resonant laser radiation in the visible region has been studied. We have detected and studied the high-energy photodesorption of iodine molecules with a translational energy of 1.4 to 1.8 eV from nanoporous quartz surfaces at an exciting photon energy ranging between 1.9 and 2.3 eV, as well as the nonequilibrium surface dissociation of molecules. Unlike the photoprocesses, which are observed only on the surface of nanoporous quartz, the thermal desorption of I₂ molecules with a considerably lower kinetic energy has also been detected on the surface of solid quartz. We have suggested a physical mechanism of photodesorption, under which electronic excitation of an iodine molecule in the confined volume of a nanopore is accompanied by a Franck-Condon electronic transition of a molecule-surface complex to a state with a higher potential energy and subsequent release of this energy in the form of kinetic energy. It has been concluded that photoprocesses on a nanostructured surface are radically different from ordinary surface photoprocesses. Zh. éksp. Teor. Fiz. 114, 114–124 (July 1998)     

Calculation of the velocity of a molecular gas slipping over a sphere with regard to accommodation coefficients

The velocity of molecular gas slipping over a spherical surface is calculated by exact analytical methods including the accommodation coefficients for the first two moments of the distribution function. An extension of the BGK approach to the Boltzmann kinetic model for the case of rotational degrees of freedom is used as the basic equation.     

固体氢的压缩行为

 同时考虑分子的平动与转动自由度，用等温等压系综的路径积分蒙特卡罗方法研究了固体氢的状态方程。在有实验数据的区域，计算结果同实验结果符合很好，在无实验数据的超高压区域，计算结果同实验的外推结果符合。为了定量研究零点运动，还计算了体系的能量。     

Rotation of molecules and the transition to turbulence

It has been discovered experimentally that the rotational degrees of freedom influence the critical Reynolds number of the transition to turbulence in a flow in a circular pipe. Pis'ma Zh. éksp. Teor. Fiz. 64, No. 1, 43–46 (10 July 1996)     

Role of highest occupied molecular orbitals in molecular field-free alignment by a femtosecond pulse

This paper studies the molecular rotational excitation and field-free spatial alignment in a nonresonant intense laser field numerically and analytically by using the time-dependent Schr?dinger equation. The broad rotational wave packets excited by the femtosecond pulse are defined in conjugate angle space, and their coefficients are obtained by solving a set of coupled linear equations. Both single molecule orientation angles and an ensemble of O₂ and CO molecule angular distributions are calculated in detail. The numerical results show that, for single molecule highest occupied molecular orbital (HOMO) symmetry σ tends to have a molecular orientation along the laser polarization direction and the permanent dipole moment diminishes the mean of the orientation angles; for an ensemble of molecules, angular distributions provide more complex and additional information at times where there are no revivals in the single molecule plot. In particular, at the revival peak instant, with the increase of temperature of the molecular ensemble, the anisotropic angular distributions with respect to the laser polarization direction of the π _g orbital gradually transform to the symmetrical distributions regarding the laser polarization vector and for two HOMO configurations angular distributions of all directions are confined within a smaller angle when the temperature of the molecular ensemble is higher.     

Semiclassical stochastic trajectory approach to molecule-solid surface scattering

A semiclassical stochastic trajectory (SST) approach to the sudy of collision induced transitions in gas molecule-solid surface scattering is presented. The time-dependent Schrödinger equation provides the time-evolution of the transition amplitudes for the molecular internal states. Classical mechanics is used to describe the molecule's center of mass motion as well as the surface atoms' motion — the latter through the generalized Langevin equation (GLE) method which allows the treatment of non-rigid surfaces (i.e. surface temperature effects). These quantum and classical equations of motion are coupled through the use of a time-dependent interaction potential in the Schrödinger equation and the use of the expectation value of the interaction potential in the classical equations of motion. Advantages of the SST approach include: (1) flexibility in the choice of quantum versus classical coordinates; (c) strict energy conservation for non-dissipative system; and (3) realistic treatment of surface many-body effects within the GLE. The SST technique is applied to the study of vibrational and rotational inelasticity in a model H₂Pt(111) system. As an initial test, results obtained assuming a rigid, smooth surface with an exponentially repulsive potential are compared to exact quantal and quasi-classical trajectory values to determine the accuracy and utility of the SST approach. A limited practical application is presented for the same H₂Pt(111) system but for a non-rigid surface. These results, calculated at low gas kinetic energies, indicate that surface energy transfer and surface temperature effects should be minimal for this type of system, even though the energy gaps are quite similar for rotational and phonon degrees of freedom.     

Helical ordering of hydrogen bonds between pairs of DNA bases

The interaction between hydrogen bonds and conformational elastic degrees of freedom has been investigated using the simplest model of a double-strand DNA molecule. The hydrogen bonds are described in terms of two-level quantum systems. After excluding conformational degrees of freedom, one has effective interaction among two-level systems. In the ground state of an ideal double helix, hydrogen bonds in a DNA molecule also have a helical order induced by conformational degrees of freedom. The pitch of the hydrogen-bond helix (and even its sign under certain conditions) is different from that of the basic helix pitch and, generally speaking, is incommensurate with the latter. This effect can, possibly, lead to an inversion of the sign of the circular dichroism in spectral bands, which was detected in some experiments. Zh. éksp. Teor. Fiz. 115, 940–950 (March 1999)     

Vibrational-rotational behavior of diatomic heteronuclear molecular systems in intense laser pulses

The dynamics of diatomic heteronuclear molecules in the low-frequency intense laser pulses is studied by numerical solution of the time-dependent Schr?dinger equation and both rotational and vibrational degrees of freedom are taken into account. The interference stabilization against the dissociation process is found to take place in a strong field and is shown to result in trapping of population in different rotational-vibrational bound states due to efficient Raman V- and ??-type transitions. The interplay between the vibrational and rotational dynamics of a molecule is investigated. The dissociation suppression due to the interference mechanism and all its attributes are established in the case of multiphoton coupling between the initial state and dissociation continuum.     

Langevin model of the rotational diffusion of molecules

Globular molecules in dense gases, liquids, and orientationally disordered crystals experience an incessant fluctuating torque of rather weak magnitude. In gases and liquids the fluctuating torque perturbs the otherwise free rotational motion which becomes diffusive. We treat the rotational diffusion within the Langevin model where the molecules are driven by a stochastic torque and hindered by a friction term. The Langevin equation for molecules with one, two, and three angular degrees of freedom is solved numerically and the dipole and Raman correlation functions are extracted. In the one-dimensional case we compare with the exact solution of the Langevin equation, in two and three dimensions with earlier work and with experimental results.