Rotational Excitation Of Diatomic Molecules Research Articles

Localization in Rotational Excitation of Diatomic Molecules Induced by a Train of Optical Pulses

Localization in Rotational Excitation of Diatomic Molecules Induced by a Train of Optical Pulses

Classical theory of rotational excitation of diatomic molecules. Rotor–rotor coupling

The new concept of two momenta coupling is developed to treat the Coriolis coupling and the centrifugal one for two rotors because they are important. A new method of classical canonical transformations is applied for two rotors coupling. The classical theory of two rotors scattering is studied. The obvious advantages of angle–action variables to describe angular momenta of the internal motion of Rotors have been employed. Canonical magnitudes of the dynamical variables have been generated by the F4 transformation function for a partly coupled set and for the fully coupled one. Such a generating function was obtained by extending Miller’s function. Relative motion of molecules is treated by classical trajectories. The theoretical model is worked out to study transport properties of gases with rotational degrees of freedom. The structure of the resulting expressions under consideration are shown to be different in principle from the expressions obtained by other approaches. The interplay between the different types of coupling influencing the transport properties is feasible to determine. The effect of coupling on energy transfer can be studied in the framework of such an approach. Previously, the usage of the approximative treatment of momentum coupling was imperative. The method is designed to incorporate recent improved formulas for calculating internal coordinates and their derivatives to ensure the most optimal calculation sequence.

Rotational excitation of diatomic molecules at intermediate energies: absolute differential state-to-state transition cross sections for electron scattering from N2, Cl2, CO and HCl

Absolute differential cross sections for the electron-impact rotational excitation of N2 Cl2, CO and HCl have been measured in a crossed-beam experiment. Results on rotational state-to-state transitions are obtained by a deconvolution procedure from the energy-loss peaks at primary energies between 10 eV and 200 eV and in the angular range from 10 degrees to 160 degrees . Details are given of an apparatus which allows absolute measurements with high-energy resolution and excellent statistics. At intermediate impact energies and scattering angles, unexpected large angular-momentum transfer was found. The results are very different for various energies and for different molecules. Four excitation mechanisms can clearly be distinguished. The experimental endings are compared with theoretical results using the semiclassical spectator model and a close-coupling calculation with an effective interaction potential.

Collisional induced rotational excitation ofN-atomic molecules

A simple model for collisional rotational excitation of diatomic molecules presented previously (in excellent agreement with experiments and computations for electron-Na2 collisions at about 300 eV) is extended toN-atomic molecules. Special attention is given to highly symmetric cases, where all molecular atoms are equivalent (with the possible exception of a different atom in the centre). Selection rules, propensity rules and rotational rainbow structures in differential state-to-state cross sections are discussed.

Rotational excitation of diatomic molecules in exothermic processes

We describe a simple model which is capable of explaining the rotational distribution of N 2 after the quenching reaction Na(3p)+N 2 → Na(3s)+N 2. Restrictions by energy and total angular momentum conservation together with the dynamics in the product valley of the potential surface determine the rotational energy transfer.

Rotational excitation of diatomic molecules in collisions with atoms

The rate constants for rotational excitation, the coefficient of RT diffusion for the Ar-N2 system, and the rotational relaxation time in N2 are calculated using the quasiclassical approximation.

Infrared pumping and rotational excitation of molecules in interstellar clouds

view Abstract Citations (92) References (23) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Infrared pumping and rotational excitation of molecules in interstellar clouds Carroll, T. J. ; Goldsmith, P. F. Abstract The effects of the rotational excitation of diatomic molecules in interstellar clouds by the absorption of infrared radiation are evaluated. A criterion for infrared pumping to alter significantly populations of the rotational states of ground and first excited vibrational levels is derived, with the effects of collisions neglected, and used to calculate the minimum required filling factor or source temperature for pumping various diatomic molecules. A model infrared source region consisting of a region of warm dust heated by embedded stars or H II regions is then developed which is characterized by an effective temperature, opacity and solid-angle dilution factor as seen by the molecular cloud, and used to derive upper limits to the size of the region affected by the infrared source. Numerical calculations for the case of the CS molecule are presented which indicate that the hot components of sources such as W3-IRS 2/2a and M17a/b emit sufficient infrared flux to perturb significantly the populations of the rotational levels. Such perturbations could lead to erroneous estimates of molecular densities if it is assumed that collisional excitation is the only operative pumping mechanism. Publication: The Astrophysical Journal Pub Date: May 1981 DOI: 10.1086/158865 Bibcode: 1981ApJ...245..891C Keywords: Infrared Radiation; Interstellar Gas; Interstellar Masers; Molecular Clouds; Molecular Excitation; Molecular Rotation; Optical Pumping; Radiative Transfer; Carbon Compounds; Diatomic Molecules; H Ii Regions; Radiation Absorption; Radiation Effects; Sulfides; Astrophysics full text sources ADS |

Theory of angular distributions of electrons resonantly scattered by molecules. I. Vibrational and rotational excitation of diatomic molecules

Resonant angular distributions for low-energy electrons scattered by diatomic molecules are derived. For homonuclear molecules, our expression for vibrational excitation is equivalent to those of others. However, we are able to clarify the role of parity favoredness. For heteronuclear molecules, our expressions are new. In particular, they contain only one parameter and are necessarily symmetric about 90\ifmmode^\circ\else\textdegree\fi{}. Furthermore, the individual rotational cross sections within the vibrational band can be determined in terms of the same parameter. Asymmetry about 90\ifmmode^\circ\else\textdegree\fi{} is predicted for these. Finally, a theorem relating these integrated rotational cross sections is derived. Results for the angular distributions are given in tabular form for easy usage.

Dynamics of the collision induced rotational excitation of diatomic molecules in a Π(-state: Classical trajectory studies for the Li 2(B 1 Π u) - Noble gas system

Rotationally inelastic collisions of noble gas atoms and electronically excited Li 2(B 1 Π u) have been studied theoretically in the classic approximation. We propose a simple potential model for the interaction between the colliding particles. Cross sections are calculated by a Monte-Carlo average over the classical trajectories. The comparison with results from laser induced fluorescence experiments is satisfactory. The dynamics of the angular momentum transfer, in particular, an orientation effect of the π-electron distribution is investigated.

The role of the collision partner in the rotational excitation of diatomic molecules

The role of the collision partner in the rotational excitation of diatomic molecules

Rotational excitation of diatomic molecules by atoms. II. Comparison of correspondence principle results with other approximations and with close-coupling results

For pt.I see ibid., vol.7, p.1916 (1974). A further study has been made of the strong-coupling correspondence principle approximation for the rotational excitation of diatomic molecules by atoms. While this approximation is expected to be most successful when the rotational quantum numbers are large, good agreement has been obtained with close-coupling results for the 0-2 total inelastic cross sections in He, Ne and Ar-N2 collisions. Comparisons with close-coupling results for other transitions in Ne-N2 and Ar-N2 collisions are generally satisfactory. The connections with other work using semiclassical methods have been clarified and the numerical comparisons possible show reasonable agreement.

Rotational excitation of diatomic molecules by atoms

The strong coupling correspondence principle is applied to the rotational excitation of diatomic molecules by atoms. The problem is formulated for arbitrary spherically symmetric atoms and molecules in Sigma states. Various limiting cases are examined and, where possible, compared with other calculations. In particular the excitation of N2 by Ne is considered and comparisons with close coupling calculations are made. It is shown that for wide ranges of quantum numbers and incident energies the methods used are accurate to within 10% and are faster by about two orders of magnitude. For greater initial excitation of the molecule the methods described should become more accurate.

Theory of collision induced rotational energy transfer in the Π-state of diatomic molecules

It is suggested that an interaction not being invariant about the internuclear molecular axis is useful for the description of rotational excitation of diatomic molecules in the electronic Pi -state. In the framework of the helicity-basis of angular momentum a complete scattering theory qualified for numerical use is presented. Collision induced excitation by rare gases, Sigma - and Pi -state molecules, are treated separately. Special attention is paid to polarization phenomena. The connection with the usual angular momentum coupling scheme is given explicitly.

Optical Potential for the Rotational Excitation of Diatomic Molecules by Atoms

By restricting attention to a single open scattering channel at a time, it is found that an optical potential, accurate to second order in the scattering potential, can be easily derived for the example of rotational excitation of a rigid rotator by a structureless atom. The resulting equations are contrasted with those derived from the close-coupling method. In cases where many open channels are present, the optical-potential method seems to offer many advantages over close coupling. Various practical methods for improving the accuracy of the optical potential beyond second order are discussed.

Adiabatic Theory of Rotational Excitation of Non-ΣStates

The formulas for the rotational excitation of diatomic molecules in the adiabatic theory are generalized to include rotational excitation within molecular states of arbitrary $\ensuremath{\Lambda}$ symmetry. For $\ensuremath{\Lambda}$ not equal to zero (non-$\ensuremath{\Sigma}$ states), the rotational quantum number can change by any integer, and not only an even integer as is the case for $\ensuremath{\Sigma}$ states.

Molecular Collisions. X. Restricted-Distorted-Wave–Born and First-Order Sudden Approximations for Rotational Excitation of Diatomic Molecules

Although a number of approximation methods have been widely used in the field of molecular rotational excitation and scattering, their interrelationships and ranges of applicability have not always been clearly established. The present work is a comparison of several of these approximations. Considered are the time-independent treatments such as the distorted wave approximation (DWA), the restricted distorted wave (RDW) and the RDW–Born approximations, and the time-dependent ones such as the sudden approximation (SA), full trajectory and straight-line limit, and the first-order perturbation approximations. Equivalence is demonstrated between the RDW–Born and first-order SA, and convenient analytical forms are presented for the resulting transition probabilities.

Rotational Excitation of Diatomic Molecules by Electron Impact

Rotational excitation of homonuclear diatomic molecules can be simply yet accurately calculated from the scattering parameters of elastic electron-molecule scattering in the fixed-nuclei approximation. The total scattering cross sections for $\ensuremath{\Delta}j\ensuremath{\ne}0$ transitions are independent of $s$-wave parameters, and ratios of $\ensuremath{\Delta}j=\ifmmode\pm\else\textpm\fi{}2$ cross sections agree with experimental results in ${\mathrm{H}}_{2}$ and with rotational close-coupling calculations. Absolute total and differential cross sections can be explained.

Computational Procedure for the Close-Coupled Rotational Excitation Problem: Scattering of Diatomic Molecules by Atoms

A computational procedure is described for the integration of the coupled differential equations and determination of the probability matrices required for the accurate evaluation of cross sections for rotational excitation of diatomic molecules. The Arthurs–Dalgarno theory of scattering of an atom by a rigid rotator is employed. The approach developed takes advantage of several of the computational schemes used in the field of electron–atom scattering, particularly those of Smith. The principal virtue of the present computational method is its capability of generating “exact” results to serve as standards against which to compare various approximations such as sudden, dominant coupling, and distorted wave.

Rotational Excitation of Diatomic Molecules by Slow Electrons: Application toH2

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Vibrational and Rotational Excitation of Diatomic Molecules. Two-Dimensional Model

The change of energy of a diatomic molecule upon collision with an atom in two dimensions was calculated. The energy contributed to the various internal degrees of freedom of the molecule was evaluated. The vibrational transition probabilities obtained were compared to experimental data for the case of O2→Ar collisions. By contrasting these results with those of a one-dimensional treatment, the form of a realistic three-dimensional potential function was predicted. It was found that at lower initial rotational energies, transfer of energy from rotational to vibrational degrees of freedom is as effective as translational→vibrational transfer. For higher initial rotational energy, rotational→vibrational transfer is shown to be less probable.