Complete determination of the photoionization dynamics of a polyatomic molecule. I. Experimental photoelectron angular distributions from à 1Au acetylene.

Angle-resolved photoelectron spectra from rotationally selected à ¹A_u 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 à ¹A_u state indicates the potential of a “complete” determination of the photoionization dynamics of the à ¹A_u state. This is further investigated in the following paper. [ABSTRACT FROM AUTHOR]