Ion-polar Molecule Collisions Research Articles

Molecular Orbital Model for Ion Polar-Molecule Capture Collisions

This article presents a molecular orbital model for ion polar molecule capture collisions which was developed by building on classical theoretical treatments. We replace the polarization potential with a perturbation molecular orbital potential, and assume that the molecular dipole does not change as a result of electron exchange at distances greater than or equal to the critical radius in the collision complex. Overlap integrals are introduced in this treatment of ion−molecule collision rates. For calculation of the perturbation molecular orbital potential, the overlap integral is approximated by use of Gaussian wave functions with scaled Slater atomic radii. The molecular dipole is assumed to be “locked” by the ion at the critical radius. The rotational mode of the molecular dipole along the locked axis is excited by coupling with the ion−molecule motion. The gain in rotational energy by the molecular dipole under the torque of the ion is approximated by a first-order Stark effect. Use of a Stark effect model results in the conservation of both energy and angular momentum. The net contribution of the ion−dipole interaction potential to ion−molecule capture collisions is to remove the rotational energy of the ion and dipole. The decrease in the ion polar molecule interaction potential caused by Stark effect excitation of dipole rotation accounts for the fact that the locked dipole approximation without Stark effect coupling significantly overestimates the rates of ion polar molecule collisions. Ab initio molecular orbital calculations on model systems were conducted to convert Slater atomic orbital radii into approximate molecular orbital radii by evaluating a scaling parameter, f. Experimental hydride transfer rates reflect the convolution of collision rates and subsequent hydride transfer rates. The reaction efficiency for hydride transfer is the ratio of the experimental reaction rate divided by the collision rate. Reaction efficiencies obtained using the collision model developed here are in qualitative agreement with Golden Rule reaction rate models. This result is in contrast with reaction efficiencies calculated by classical potentials that show a monotonic increase in reaction efficiency with increasing reaction free energy.

Parametrization of kinetic energy dependences of ion–polar molecule collision rate constants by trajectory calculations

Kinetic energy dependences of ion–polar molecule capture rate constants have been calculated using the trajectory method at varies temperatures. An empirical equation was formulated to fit the calculated data. The parametrized equation gives rate constants within 5% error for re- lative kinetic energies ranging from thermal to several eV and temperatures ranging from 50 K to 1000 K.

The effect of the dipole-induced dipole potential on ion–polar molecule collision rate constants

The effect of the dipole-induced dipole potential on ion–polar molecule collision rate constants

Trajectory calculations of high temperature and kinetic energy dependent ion–polar molecule collision rate constants

The trajectory method is used to calculate high temperature and kinetic energy dependent ion–polar molecule collision rate constants. A new ion–polar molecule interaction potential energy surface is derived which takes into account the average hard sphere diameter of the colliding partners and the dimensions of the permanent dipole and the induced dipole vectors. A model system, H+3+NH3 is chosen for the calculation. The calculated results show that at low temperatures and kinetic energies, the effects of the size of the ion–molecule partners and the dimensions of the dipole vectors on the collision rate constant are small. At high temperature and high relative kinetic energies, however, these effects are significant. The calculated results are in good agreement with existing experimental kinetic energy dependent reaction rate constants.

Trajectory calculations of the effect of the induced dipole–induced dipole potential on ion–polar molecule collision rate constants

Trajectory calculations of the effect of the induced dipole–induced dipole potential on ion–polar molecule collision rate constants

Parametrization of the ion–polar molecule collision rate constant by trajectory calculations

A recently reported calculation by chesnavich, Su and Bowers on classical trajectory study of thermal energy ion-polar molecule capture collisions is further extended. (AIP)

Rotational Excitation of Symmetric-Top Molecules by Low-Energy Ion Impact

Theory of collisions between ions and symmetric-top molecules is formulated. This work is to investigate the adiabatic nature of low energy ion-polar molecule collisions. When the angular momentum quantum number projected on the symmetry axis of symmetric-top molecules is not zero, the elastic collision is significantly different from that where the molecule is linear, but not so much for the inelastic collision. Some discussions about the scaling law obtained by Takayanagi and about the modified Born approximation are given.

On statistical and thermodynamic approaches to ion polar molecule collisions

Capture collision rate constants for ion polar molecule systems obtained from an average free energy function are shown to be equivalent to those obtained from a canonical activated complex theory formalism. Results provide a satisfactory least upper bound for observed reaction rate constants and compare well with Chesnavich, Su, and Bowers’ results obtained using microcanonical variational transition state theory. The average free energy approach is extended to the ion–quadrupole interaction, and capture collision rate constants are obtained providing a satisfactory least upper bound on experimental rate constants. A thermodynamic model for ion polar neutral collisions is developed and the difference between capture collision rate constants and momentum transfer collision rate constants rationalized in terms of a repulsive entropic force which prevents capture but produces isotropic scattering. The success of the results of Barker and Ridge in accounting for momentum transfer rates is thus explained and connected to the success of the average free energy result in accounting for reaction rate constants. It is argued that the agreement between theory and experiment indicates that rotational inelasticity plays a significant role in a gas phase transport property, i.e., the momentum transfer collision rate of ions in polar gases.

Low-Energy Ion-Polar Molecule Collision –Further Study in Perturbed Rotational State Approach–

A good convergency of the semiclassical PRS method, developed recently by K. Takayanagi (J. Phys. Soc. Jpn. 45 (1978) 976, referred to as I), has been confirmed. The straight-line trajectory treatment has proved to be a good approximation for the low-energy ion-polar molecule collision where the long-range dipole interaction is dominant. A scaling low derived in I is found useful for predicting rotational excitation cross sections for a large number of collision pairs.

Ion-polar molecule collision frequency. A thermodynamic treatment

Ion-polar molecule collision frequency. A thermodynamic treatment

Energy transfer in ion-polar molecule collisions

Rotational excitation of HCN in collisions with Na + is considered, at energies between 0.1 and 10 eV using a point charge rotating dipole, impact parameters description. The resulting cross sections are interpreted in terms of crossings between Stark-shifted rotational levels. In the region where inelastic collisions dominate, non-polar molecule reactions should proceed through complex formation. The model predicts the same behavior as orbiting models at lower energies, yielding a rate independent of temperature, in agreement with experiment.

Ion–polar molecule collisions. Conservation of angular momentum in the average dipole orientation theory. The AADO theory

The average dipole orientation (ADO) theory for capture collisions between ions and dipolar molecules is modified to include conservation of angular momentum approximately; termed AADO theory. The AADO theory is compared to experiment for proton transfer reactions from various positive ions to NH3, HCN, and CH3CN substrates and for several negative ions to HCN. The agreement between theory and experiment is quite good in all cases. The AADO rate constants are larger than the ADO rate constants in all cases. For the systems studied the average increases in AADO rate constants over ADO values were 12% (NH3), 20% (HCN), and 31% (CH3CN). For most polar molecules, AADO predictions should be about 10%–30% larger than ADO values. The theory has been parameterized in the form kAADO= (2πq/μ1/2)[α1/2+CμD (2/πkT)1/2+(ZμDI1/2/α1/4)], where the first two terms are simply kADO and the last term comprises the correction due to angular momentum conservation. The constant C is the ADO dipole locking constant. The constant Z is a function of temperature only and a table of Z values for a wide temperature range is given. For molecules with moments of inertia I?1×10−39g cm2 a somewhat different parameterized equation must be used. As part of the development of the AADO theory, a comparison is made between ADO theory and a recent treatment of Barker and Ridge. A number of recommendations are made for modifying the Barker–Ridge approach. Implementation of these modifications brings essential agreement between the Barker–Ridge approach and the ADO theory.

Low-Energy Ion-Polar Molecule Collision –The Perturbed Rotational State Approach–

Ion-Polar molecule collisions are studied in the Perturbed Rotational State approach. The basic idea is that the molecular rotation is nearly adiabatically deformed during the collision. The semiclassical, impact-parameter method is adopted. This formulation of the collision problem gives an easy way to calculate the rotational excitation cross sections. Numerical examples are given for the low-energy collision between a proton and a CN molecule. A scaling law is derived so that the numerical results obtained can be used also for many other collision systems.

Ion-polar molecule collisions. A modification of the average dipole orientation theory: The [formula omitted] model

The average dipole orientation (ADO) theory of ion-polar molecule capture collisions is reformulated in terms of the average cosine, cos θ . The earlier formulation used an average angle, θ , in the effective potential that is used to develop expressions for the cross section and rate constant. The cos θ and θ models give virtually identical results for thermal energy capture rate constants.

Ion-polar molecule collisions: Nonreactive collisions of Cl− with dichloroethylene and difluorobenzene

Momentum transfer rate constants for Cl− with dichloroethylene and difluorobenzene isomers have been studied by an ion cyclotron resonance line-broadening technique. Rate constants for nonpolar isomers are compared to those predicted by the Langevin theory and the rate constants for polar molecules are compared to the average-dipole-orientation (ADO) theory. All experimental rate constants are consistently higher than theoretical predictions. The incremental effect of a permanent dipole on momentum transfer collision frequencies predicted by ADO theory is in satisfactory agreement with experimental results.

Ion-polar molecule collisions. Proton transfer reactions of butyl ions with ammonia, methylamine, diethylamine, and trimethylamine

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTIon-polar molecule collisions. Proton transfer reactions of butyl ions with ammonia, methylamine, diethylamine, and trimethylamineTimothy. Su and Michael T. BowersCite this: J. Am. Chem. Soc. 1973, 95, 23, 7611–7613Publication Date (Print):November 1, 1973Publication History Published online1 May 2002Published inissue 1 November 1973https://doi.org/10.1021/ja00804a012RIGHTS & PERMISSIONSArticle Views86Altmetric-Citations21LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (347 KB) Get e-Alerts Get e-Alerts

Theory of ion-polar molecule collisions. Comparison with experimental charge transfer reactions of rare gas ions to geometric isomers of difluorobenzene and dichloroethylene

A classical theory for the ion-permanent dipole interaction is developed that takes into consideration the thermal rotational energy of the polar molecule. The theory is formulated in terms of an r-dependent average orientation angle θ̄ (r) between the dipole and the line of centers of collision. The technique allows quantitative determination of the capture cross section as a function of ion-polar molecule relative velocity. In addition, capture limit rate constants are readily calculated both at thermal energies and as a function of relative energy. Charge transfer rate constants from various rare gas ions to difluorobenzene and dichloroethylene isomers have been measured at thermal energies using ion cyclotron resonance spectroscopy. Rate constants are considerably larger than predicted by the capture theories for both polar and nonpolar isomers indicating long range electron jump is a prevalent mechanism for charge transfer in these systems. The average-dipole-orientation theory developed in this paper adequately accounts for the effects of the permanent dipole moment on the rate constant.

Ion-polar molecule collisions. Proton transfer reactions of H3+ and CH5+ to the geometric isomers of difluoroethylene, dichloroethylene, and difluorobenzene

Ion-polar molecule collisions. Proton transfer reactions of H3+ and CH5+ to the geometric isomers of difluoroethylene, dichloroethylene, and difluorobenzene