Dawes Research Group
Spin-Forbidden Chemistry
The ground and first excited states of HCO are coupled and degenerate for linear geometries. This Renner-Teller coupling plays an important role in the photodissociation dynamics and can even affect the spectroscopy of the bound-state levels on the ground state.
The spin-forbidden chemistry of the O(3P) + CO → CO2 reaction is studied using three automatically generated PESs. (left) Two frustrated triplet states which correlate with ground state O(3P) have shallow wells hanging above the deep singlet CO2 well. The spin-forbidden reaction occurs via spin-orbit coupling between the surfaces. (right) The rate of spin-forbidden formation in the high-pressure limit is calculated to be 7-35 times larger than previous models.
Ahren W. Jasper and R. Dawes, J. Chem. Phys. 139, 154313 (2013).
van der Waals Systems
Using our interpolative fitting methods, combined with explicitly correlated ab initio methods, we have fit highly accurate PESs for a series of vdWs systems. The PESs have been used to compute ro-vibrational bound states, as well as state-to-state scattering cross-sections. Interestingly we have found that low-energy channels in some of the PESs correspond to unusual scattering propensities.
Potential Energy Surfaces (PES)
Our research involves theoretical studies of the spectroscopy and dynamics of small molecules in the gas phase relevant to atmospheric, interstellar and combustion chemistry.
Current projects combine developments in the areas of PES fitting and multistate multireference quantum chemistry to allow spectroscopically and dynamically/kinetically accurate investigations of key molecular systems many of which are radicals with strong multireference character and have the possibility of multiple electronic states contributing to the observed dynamics.
We develop PES fitting methods using interpolation (IMLS) in which generations of new data are added automatically by an algorithm, refining the fit towards negligible error.
Ozone
We have developed an accurate PES for ozone overcoming a spurious submerged reef feature common in previous PESs.
Having the correct topography proved critical. In collaboration with Hua Guo (New Mexico) and Zhigang Sun (Dalian) we have studied the state-to-state reaction dynamics, reproducing the experimentally observed negative temperature dependence of isotope exchange rates.
Steve Ndengue, Richard Dawes, Xiaogang Wang, Tucker Carrington Jr., Zhigang Sun and Hua Guo, Calculated vibrational states of ozone up to dissociation, J. Chem. Phys. 144, 074302 (2016).
Zhigang Sun, Dequan Yu, Wenbo Xie, Jiayi Hou, Richard Dawes, Hua Guo, J. Chem. Phys. 142, 174312 (2015).
Wenbo Xie, Lan Liu, Zhigang Sun, Hua Guo, Richard Dawes, J. Chem. Phys. 142, 064308 (2015).
Yaqin Li, Zhigang Sun, Bin Jiang, Daiqian Xie, Richard Dawes, Hua Guo, J. Chem. Phys. 141, 081102 (2014).
Richard Dawes, Phalgun Lolur, Anyang Li, Bin Jiang and Hua Guo, J. Chem. Phys. 139, 201103 (2013).
PES plots for CO-dimer (left) and CO2-dimer (right) showing low-energy channels for geared motion.
State-to-state scattering cross-sections for CO-CO collisions (computed using MCTDH) predict that symmetric excitations are strongly favored.
Steve A. Ndengué, Richard Dawes and Fabien Gatti, J. Phys. Chem. A 119, 7712 (2015).
Richard Dawes, Xiao-Gang Wang and Tucker Carrington Jr., J. Phys. Chem. A, 117, 7612 (2013).
Recently we have used a large DVR grid of more than 24 million functions to compute all of the bound vibrational states.
Wavefunction plots for the (1,1,1) and (0,11,1) states.
D0 = -225.7 cm-1
D0 = -136.8 cm-1
D0 = -126.7 cm-1
Some high-lying states delocalized into all three symmetry equivalent wells, with amplitudes extending towards dissociation.
For more details about these and many other projects, please see
Publications
We thank the DOE and NSF for their generous support.
DE-SC0010616
CHE-1300945