Vibrational and shake-up excitations in the C 1s photoionization of ethane and deuterated ethane

The absolute photoabsorption spectra of ethane (C2H6), encompassing the C 1s-1 3p excitation, the C 1s threshold and the satellite thresholds is measured. Further, photoelectron spectra are taken in the region from the C 1s threshold region up to 380 eV, and the vibrational fine structure and C 1s-1 partial cross section studied. The complex vibrational fine structure for both ethane and deuterated ethane (C2D6) is analysed using a coupled least-squares fit procedure. While we cannot exclude the presence of the C-C stretching mode (3), the experimental data show that the C 1s photoelectron spectrum is dominated by two vibrational modes, the C-H stretch 1 and the C-H deformation mode 2. Compared with their values in the neutral ground state there is a significant increase in the vibrational energies to 407±5 meV and 176±5 meV for ethane and 291±10 meV and 130±10 meV for deuterated ethane, respectively. The lifetime broadening is determined to be 98±10 meV, which is in good agreement with calculations. The investigated shake-up structure closely resembles that of methane. The lowest-lying satellite band gains intensity towards threshold which may be attributed to conjugate shake-up processes.