Inelastic collisions of slow electrons with SrBr<Subscript>2</Subscript> molecules

Inelastic collisions of slow electrons with SrBr₂ molecules were studied experimentally. The dissociative excitation cross sections of two lines of the strontium atom and eight lines of the singly charged strontium ion were measured. Six optical excitation functions were recorded over the electron energy range 0–100 eV. Dissociative excitation cross sections were also measured for two strontium monobromide sequences related to the B ²Σ⁺-X ²Σ⁺ system.     

The dissociative excitation of singlet and quintet nickel atom states in e-NiBr<Subscript>2</Subscript> collisions

The dissociative excitation of singlet and quintet nickel atom states in e-NiBr₂ collisions was studied by the method of extended intersecting beams. Optical excitation functions over the electron energy range 0–100 eV were recorded for most of the spectral lines observed. Possible dissociative excitation channels at low electron energies were discussed. The cross sections of dissociative and direct excitations and dissociative excitations of the NiBr₂ and NiCl₂ molecules were compared.     

The dissociative excitation of cobalt atom even sextet levels in collisions of electrons with CoCl2 molecules

The cross sections of dissociative excitation of 46 transitions from cobalt atom even sextet levels in collisions of electrons with CoCl₂ molecules were measured at an exciting electron energy of 100 eV. The dissociative and direct CoI excitation cross sections were compared. The results were used to calculate the total cross sections of dissociative excitation of CoI levels at an electron energy of 100 eV. Possible reaction channels at low electron energies are discussed.     

II. Electron-impact dissociative excitation of C<Subscript>2</Subscript>H<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack> and C<Subscript>2</Subscript>D<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack>

Absolute cross-sections for electron-impact dissociative ionization of C₂ H₂⁺ and C₂ D₂⁺ to CH⁺, C⁺, C₂⁺ , H⁺, CH₂⁺ and C₂D⁺ fragments are determined for electron energies ranging from the corresponding threshold to 2.5 keV. Results obtained in a crossed beams experiment are analyzed to estimate the contribution of dissociative ionization to each fragment formation. The dissociative ionization cross sections are seen to decrease for more than an order of magnitude, from CH⁺ (5.37±0.10) × 10^-17 cm² over C⁺ (4.19± 0.16) × 10^-17 cm², C₂D⁺ (3.94±0.38) × 10^-17 cm², C₂⁺ (3.82±0.15) × 10^-17 cm² and H⁺ (3.37±0.21) × 10^-17 cm² to CH₂⁺ (2.66±0.14) × 10^-18 cm². Kinetic energy release distributions of fragment ions are also determined from the analysis of the product velocity distribution. Cross section values, threshold energies and kinetic energies are compared with the data available from the literature. Conforming to the scheme used in the study of the dissociative excitation of C₂H₂⁺ ( C₂ D₂⁺ )\left( {\rm C}_2 {\rm D}_2^+ \right), the cross-sections are presented in a format suitable for their implementation in plasma simulation codes.     

Luminescence excitation in reactive molecular CO + O<Subscript>2</Subscript> collisions on the surface of Y<Subscript>2</Subscript>O<Subscript>3</Subscript>-Eu

It is shown that the CO + O₂ → CO₂ catalytic reaction on the surface of Y₂O₃-Eu may lead to electronic excitation of Eu³⁺ luminescence centers due to the chemical energy release. The luminescence observed allows one to study the interaction between molecular particles of ultralow (thermal) energies with surface by optical methods.     

The dissociative excitation of odd doublet cobalt atom levels in collisions of electrons with cobalt dichloride molecules

The extended crossed beam method was used to measure the dissociative excitation cross sections in e-CoCl₂ collisions for 91 transitions from odd doublet levels of cobalt atoms. The dissociative and direct CoI excitation cross sections were compared. Possible reaction channels at low electron energies were considered. The results were used to calculate the total dissociative excitation cross section of CoI levels at an exciting electron energy of 100 eV. For the z ² F°, z ² G°, and y ² G° levels, cascade population contributions were also determined.     

Kinetics of low-temperature initiation of H<Subscript>2</Subscript>/O<Subscript>2</Subscript>/H<Subscript>2</Subscript>O mixture combustion upon the excitation of molecular vibrations in H<Subscript>2</Subscript>O molecules by laser radiation

The initiation of H₂/O₂/H₂O mixture combustion when asymmetric vibrations in H₂O molecules are excited by a resonant IR laser radiation is considered. It is shown that the vibrational excitation of the molecules gives rise to new efficient channels for the formation of chemically active O and H atoms and OH radicals. As a result, the chain mechanism of combustion in the mixtures is enhanced and, as a consequence, the induction time is cut and the ignition temperature is lowered. Even at a minor radiant energy flux delivered to the gas (E_in≈2.5 J/cm²), the ignition temperature of the stoichiometric H₂/O₂ mixture containing only 5% of H₂O may become as low as 300 K.     

The dissociative excitation of doublet and sextet manganese atom levels in collisions of electrons with manganese dibromide molecules

Inelastic collisions of electrons with manganese dibromide molecules were studied by the method of extended crossing beams. These collisions cause the formation of excited manganese atoms in doublet and sextet states. At an exciting electron energy of 100 eV, 52 dissociative excitation cross sections were measured. At electron energies 0–100 eV, three optical excitation functions were recorded. The ratio between excitation cross sections in electron-molecular and electron-atomic collisions is considered.     

Rotational excitation of NH<Subscript>3</Subscript> and ND<Subscript>3</Subscript> due to He atom collisions

Quantum close-coupling and coupled-states approximation scattering calculations for rotational energy transfer of rotationally excited NH₃ and ND₃ due to collisions with He are presented. Calculations were performed for collision energies between 10^-5 and 10 000 cm^-1 using the NH₃-He potential of Hodges and Wheatley [J. Chem. Phys. 114, 8836 (2001)]. State-to-state and total quenching cross sections from some selected initial states are presented. Rate coefficients for ortho-NH₃ for the quenching 10+→00+ transition were obtained on potentials scaled to reproduce measurements of second virial coefficients with the results showing strong sensitivity to the potential, especially at low temperatures. Significant isotope effects are found in quenching cross sections in the cold to ultracold regime particularly in the region dominated by quasi-bound resonances, ~0.1 to 10 cm^-1. As ammonia has been translationally cooled via Stark deceleration methods, it is a good candidate for experimental study of such effects at cold temperatures. Comparison of rate coefficients with available theoretical results are also presented.     

III. Electron-impact dissociative ionization of C<Subscript>2</Subscript>H<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack> and C<Subscript>2</Subscript>D<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack>

The dynamics of cold atoms in conservative optical lattices obviously depends on the geometry of the lattice. But very similar lattices may lead to deeply different dynamics. In a 2D optical lattice with a square mesh, it is expected that the coupling between the degrees of freedom leads to chaotic motions. However, in some conditions, chaos remains marginal. The aim of this paper is to understand the dynamical mechanisms inhibiting the appearance of chaos in such a case. As the quantum dynamics of a system is defined as a function of its classical dynamics – e.g. quantum chaos is defined as the quantum regime of a system whose classical dynamics is chaotic – we focus here on the dynamical regimes of classical atoms inside a well. We show that when chaos is inhibited, the motions in the two directions of space are frequency locked in most of the phase space, for most of the parameters of the lattice and atoms. This synchronization, not as strict as that of a dissipative system, is nevertheless a mechanism powerful enough to explain that chaos cannot appear in such conditions.     

Luminescence in collisions of low-energy ions with graphite and Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

Excitation of H⁺, H₂ ⁺, H₃ ⁺, He⁺, and Ar⁺ ions by impact on graphite and Al₂O₃ was investigated by means of emission spectroscopy in the 50–1000 eV energy range of the projectiles. Emission of Balmer series from excited neutral hydrogen is observed for both targets. In addition, for the Al₂O₃ target a continuum emission is observed. The continuum probably originates from excited M_nO_m molecules produced in the collision cascade, when surface atoms bound by ionic bonds are released after the bond breaking caused by neutralization. The spectra obtained under Ar⁺ -bombardment show Ar II lines emitted by backscattered ions.     

Electronic excitation energy transfer between dye molecules in H<Subscript>2</Subscript>O and D<Subscript>2</Subscript>O solutions in the micellar phase

Processes of electronic excitation energy transfer (EEET) in H₂O+D₂O solutions within reversed micelles with different degrees of hydration were studied. It is ascertained that the structure of solutions forms a cluster distribution of interacting molecules having a fractal dimensionality. As a result, in regions with a locally high concentration of the dye molecules, an increase in the EEET efficiency is observed. Solubilization by reversed micelles leads to destruction of the cluster structure of the water system, with the dependence of the EEET efficiency on the degree of hydration being nonmonotonic. As the degree of hydration increases, the inhomogeneities of the structure inherent in bulk water are restored.     

Anomalous absorption in H<Subscript>2</Subscript>CN and CH<Subscript>2</Subscript>CN molecules

Structures of H₂CN and CH₂CN molecules are similar to that of H₂CO molecule. The H₂CO has shown anomalous absorption for its transition 1₁₁–1₁₀ at 4.8 GHz in a number of cool molecular clouds. Though the molecules H₂CN and CH₂CN have been identified in TMC-1 and Sgr B2 through some transitions in ortho as well as in para species, here we have investigated the condition under which transitions 1₁₁–1₁₀ and 2₁₂–2₁₁ of these molecules may show anomalous absorption. For the present investigation, we have calculated energy levels and radiative transition probabilities. However, we have used scaled values for collisional rate coefficients. We found that relative values of collisional rate coefficients can produce the required anom-alous absorption in 1₁₁–1₁₀ and 2₁₂–2₁₁ transitions in the molecules.      

Polarizability of two interacting molecules N<Subscript>2</Subscript> and O<Subscript>2</Subscript>

In the context of the Silberstein theory, by introducing model atoms, the polarizability of pairs of interacting molecules N₂-N₂, O₂-O₂, and N₂-O₂ was studied in relation to the mutual orientation and the intermolecular distance of the molecules in the pairs. The polarizability tensor for the equilibrium configurations of the (N₂)₂ and (O₂)₂ dimers was calculated.     

Dissociation-induced excitation of CsII in collisions of electrons with CsOH molecules

Dissociation-induced excitation of a singly charged cesium ion taking place as a result of collisions of electrons with CsOH molecules is investigated. Possible reaction channels in the low-energy region are discussed. It is established that sequential population plays an important role for 6p levels of Cs⁺. Moscow Power Engineering Institute, 14, Krasnokazarmennaya St., Moscow, 111250, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 2, pp. 159–165, March–April, 1998.