Theoretical calculation of positron annihilation spectrum using positron-electron correlation-polarization potential

The positron-electron correlation-polarization potential model is used to calculate annihilation spectra of carbon disulfide and benzene. We assume that the positron is captured in the vibrationally excited states of the target molecule through vibrational Feshbach resonances. Using the standard normal mode representation, we calculated the resonance energies and widths for each vibrational mode. The resonance widths were calculated with Fermi's Golden Rule approximation, where the time-dependent wave packet approach has been applied. We found that vibrational resonances of infrared-active modes play a dominant role in resonant annihilation; however, infrared-inactive modes also contribute to the annihilation spectrum through polarizability changes along normal mode coordinates.