Robert Parson

Lab: Cristol Chemistry


Ph.D.: University of Michigan, 1984
Fellow of the Joint Institute for Laboratory Astrophysics (JILA)

Areas of Expertise

Reaction Dynamics, Theoretical Chemistry

Theoretical Dynamics of Molecules and Clusters

Professor Parson's research group generally focuses on a few related problems at any given time, but the analysis of these problems involves a wide variety of theoretical concepts and techniques ranging from ab initio electronic structure calculations, to classical and quantum molecular dynamics simulations, to purely analytical theory. Most of the problems under investigation are closely tied to experimental work at CU or elsewhere.

One area of activity is the structure and dynamics of molecular cluster ions. When a molecular ion, such as I2-, is embedded in a cluster of neutral but polar or polarizable molecules, such as CO2, the electronic structure of the ion is strongly perturbed by the electrostatic interaction with the surrounding "solvent" molecules. As a result, photodissociation of the ion inside the cluster yields dynamics that has no analog in either the gas phase or in neutral clusters. As the ion dissociates, a charge distribution which was originally delocalized becomes localized on a single atom; the solvent responds to this changing charge distribution, and the subsequent combination and relaxation dynamics are dominated by long-range, col-43 lective forces that are qualitatively different from the forces that operate in neutral clusters. In order to treat a problem like this theoretically, one must compute the electronic structure of the ion as it is perturbed by the cluster environment; this means carrying out an electronic structure calculation inside a molecular dynamics simulation. The group has developed an Effective Hamiltonian technique that allows such calculations to be carried out quickly and accurately, and allows the calculation of properties that can be directly compared with experiments carried out at CU and elsewhere.

Another area of research is energy in molecular collisions, particularly in large molecules and molecular Experiments have shown that rotational energy transfer in collisions of highly symmetric molecules, such as methane and silane, is remarkably selective, in that only a small fraction of the accessible final states are populated. The group has shown that this selectivity can be understood by considering the effects of centrifugal and Coriolis forces in the rapidly rotating molecules. A new project involves collisions between hydrated hydronium and hydrated hydroxide ions, comparing the different mechanisms for neutralization in small and large clusters.

N. Delaney, J. Faeder, and R. Parson "Photodissociation and Recombination of solvated I2-: What causes the transient absorption peak?" J. Chem. Phys.111, 452, 1999.

N. Delaney, J. Faeder, and R. Parson "Simulation of UV photodissociation of I2-· (CO2)n : Spin-orbit quenching via solvent mediated electron transfer", J. Chem. Phys.111, 651, 1999.

S. Nandi, A. Sanov, N. Delaney, J. Faeder, R. Parson, and W. C. Lineberger, "Photodissociation of I2-· (OCS)n cluster ions: Structural implications" J. Phys. Chem. A102, 8827, 1998.

J. Faeder, N. Delaney, P. E. Maslen, and R. Parson, "Modeling Structure and Dynamics of Solvated Molecular Ions: Photodissociation and Recombination in I2-· (CO2)n", Chemical Physics, 239, 525, 1998.

P. E. Maslen, J. Faeder and R. Parson, "An Effective Hamiltonian for an Electronically Excited Solute in a Polarizable Molecular Solvent", Molecular Physics94, 693, 1998.

J. Faeder and R. Parson, "Ultrafast Reaction Dynamics in Cluster Ions: Simulation of the Transient Photoelectron Spectrum of I2- Ar n Photodissociation", J. Chem. Phys., 108, 3909, 1998.

B. Ladanyi and R. Parson, "Structure and Dynamics of Molecular Ions in Clusters: I2- in flexible CO2", J. Chem. Phys., 107, 9326, 1997.

R. Parson and J. Faeder, "Ultrafast reaction dynamics in molecular cluster ions", Science276, 1660, 1997.