James J. Munro

Quantemol-N: an expert system for performing electron molecule collision calculations using the R-matrix method

The R-matrix method has been widely employed to ab initio calculations on a large variety of problems related to electron molecule scattering. The UK Molecular R-matrix Code, which are a synthesis between codes designed for quantum chemistry and electron atom scattering calculations, has proved particularly popular for these studies but is difficult for the non-specialist to use. The Quantemol-N software environment is designed for scientists with a minimal knowledge of scattering theory or quantum chemistry to use without the need of a complex and dedicated training. Their use is illustrated for low energy electron collisions with silane.

Resonant states of H3+ and D2H+

Vibrational resonances for H(3) (+) and D(2)H(+), as well as H(3) (+) at J=3, are calculated using a complex absorbing potential (CAP) method with an automated procedure to find stability points in the complex plane. Two different CAP functional forms and different CAP extents are used to analyze the consistency of the results. Calculations are performed using discrete variable representation continuum basis elements calculated to high levels of accuracy by diagonalizing large, dense, Hamiltonian matrices. For D(2)H(+), two energy regions are analyzed: the one where D(2)+H(+) is the only dissociation product and the one where HD+D(+) can also be formed. Branching ratios are obtained in the latter case by using different CAPs. It is shown that H(3) (+) and D(2)H(+) support some narrow Feshbach-type resonances but that higher angular momentum states must be studied to model the pre-dissociation spectrum recorded by Carrington and co-workers [J. Chem. Phys. 98, 1073 (1993)].

Properties of high-lying vibrational states of the molecular ion

Calculations are presented for the vibrational states of on a potential with the correct dissociation properties (Molec. Phys., 98, 261 (2000)) using both Radau and Jacobi coordinates. This potential is found to support horseshoe states at low to intermediate energies. Near the dissociation limit a new class of long-range states, called asymptotic vibrational states (AVS), is found. These states are similar to those suggested to explain the observed near-dissociation spectrum of . The possible consequences of such states are discussed.

Asymptotic vibrational states of the H3+ molecular ion

Vibrational calculations for H + are performed using an accurate global ab initio potential energy surface. Fourteen bound states close to dissociationarefoundtohaveinterestinglong-rangedynamics.Theseasymptotic vibrational states (AVS) are studied graphically by cuts through their wave functionsandbycalculatingarotationalconstant.TheseAVS,whichoverlapopen systemclassicaltrajectoriesthatformhalf-tori,shouldleadtoanincreaseddensity of states near dissociation. Their influence on the infrared near-dissociation spectrum of H + remains to be determined.

The role of asymptotic vibrational states in

Calculations are discussed which characterize all the vibrational bound states of the and D2H+ molecular ions using a realistic ab initio potential energy surface. Graphical analysis and calculation of rotational constants show that both ions support a series of atom–diatom-like long-range states: asymptotic vibrational states. The role of these states in the system and other molecules is discussed. The vibrational calculations are extended above dissociation where the resulting (Feshbach) resonances are shown to be too short-lived to be of importance for the photodissociation spectrum.

A dissociative electron attachment cross-section estimator

Dissociative electron attachment (DEA) is the major process where molecules are destroyed in low-energy plasmas. DEA cross sections are therefore important for a whole variety of applications but are both hard to measure or compute accurately. A method for estimating DEA cross sections based a simple resonance plus survival model is presented. Test results are presented for DEA of molecular oxygen and molecular chlorine, for which experimental measurements are available for comparison, and SiBr and SiBr2, for which no previous data is available. The estimator has been implemented as part of Quantemol-N expert system which uses the R-matrix method to predict resonance positions and widths.

Global plasma simulations using dynamically generated chemical models

Extensive molecular data are a key requirement in understanding modern technical plasmas. A method for coupling molecular data with chemical models in a global plasma simulation to enable rapid testing and evaluation of new plasmas is presented. A global plasma model (GLOBALKIN) is extended using an expert system (Quantemol-P) to enable ad hoc simulations using new plasma recipes. A set of atomic and molecular species to be considered in the plasma simulation is specified by the user. The expert system generates a complete set of reaction pathways for both the gas and surface reactions in a plasma. This set is pruned by discarding unphysical reactions and reaction data not appropriate to technical plasmas (such as autodetachment). The species, gas phase reactions, surface reactions, and plasma properties can be adjusted to control the simulation. The reaction list is populated through a database of molecular parameters and cross sections; missing data can be calculated through molecular cross sections usi...

Ab initio spectroscopy of D2H+ near dissociation

Extensive calculations for the vibrational band origins of D2H+ up to dissociation are presented. Due to the high density of vibrational states near dissociation, huge basis sets needed to be used as well as massively parallel computers. We have found 1209 A1 and 1078 B1 bound states, some of which display long-range features, which are analysed in detail. The calculations were performed within the Born–Oppenheimer approximation and non-adiabatic corrections to it are evaluated. However, the main source of error for the states near dissociation arises from the Potential Energy Surface at high energies.

Simulations of SF 6 plasma etching in the GEC Reference Cell

Here we present 2D simulations of an inductively driven SF6 silicon etch process in the GEC Reference Cell, performed with Quantemol-D and building upon previous calculations of SF6 plasma chemistries using Quantemol-P. Pressure and power trends along with chamber wide contour plots of gas-phase species concentrations and fundamental plasma properties are considered. We find good agreement with experimental results, which both validates the underlying model and points to the important role of simulation-assisted plasma process development and optimization.