High Harmonic Generation from biological molecules
High Harmonic molecular spectra provide insights into attosecond electronic dynamics in the target molecule. Accurate values of the dipole matrix elements between bound and continuum molecular states are required to generate the spectra. This STSM has allowed Zdeněk Mašín to learn to use the codes developed at Max Born Institute to generate the dipole matrix elements from the results of the R-matrix calculations and to apply them to calculations of photoionization cross sections.
The calculations were performed using the UKRmol suite of codes implementing the molecular R-matrix method. In order to benchmark the quality of our calculated dipole matrix elements for pyrazine we calculated the photoionization cross sections and photoelectron angular distributions (shown in the Figure). The results, performed using a simple Close-Coupling model including the lowest-lying 40 electronic states, show an encouraging agreement with previous experiments and theory. However, the description of the correlation/polarization interaction was limited in this model and therefore the shape resonances, such as the broad resonance in the 6ag cross section, appear too high in energy. This deficiency will be removed in more sophisticated models which we are developing.
This STMS has allowed us to obtain the first photoelectron angular distributions for pyrazine and to identify directions for further improvement of our calculations so that accurate High Harmonic spectra can be obtained. The next steps in the collaboration will include:
- Improving on the target CI description in the scattering calculations by including dynamical correlation.
- Calculating the population transfer in the target cation induced by the laser field.
- Analyzing the Dyson orbitals generated using the R-matrix codes.
- Generating the High Harmonic spectra.