Complete determination of the photoionization dynamics of a polyatomic molecule. I. Experimental photoelectron angular distributions from A1Au acetylene.

ABSTRACT

Angle-resolved photoelectron spectra from rotationally selected A1Au state acetylene have been recorded using velocity-map imaging. Several Renner-Teller split vibrational bands have been observed and assigned, showing good agreement with previous zero kinetic energy photoelectron (ZEKE) work [S. T. Pratt, P. M. Dehmer, and J. L. Dehmer, J. Chem. Phys. 99, 6233 (1993); S.-J. Tang, Y.-C. Chou, J. J.-M. Lin, and Y.-C. Hsu, ibid. 125, 133201 (2006).] The extracted photoelectron angular distributions (PADs) corresponding to these bands show a strong dependence on the vibronic angular momentum projection quantum number K+. Subbands with odd K+ show PADs with maximum intensity along the polarization vector of the ionizing laser beam, while those with even K+ show PADs with maximum intensity perpendicular to this direction. Velocity-map images recorded at low photoelectron energies approach rotational resolution of the ion, and the evolution of the PADs with increasing rotational level prepared in the A1Au state indicates the potential of a "complete" determination of the photoionization dynamics of the A1Au state. This is further investigated in the following paper.