1+1 PFI-ZEKE PHOTOELECTRON SPECTROSCOPY OF $C_{2}H_{2}$-THE RENNER-TELLER EFFECT OF $C_{2}H^{+}_{2}$

Author Institution: Institute of Atomic and Molecular Sciences, Academia Sinica; Department of Chemistry, National Taiwan UniversityThis paper presents the 1+1 pulsed-field induced zero-kinetic energy (PFI-ZEKE) photoelectron spectrum of $C_{2}H_{2}$ recorded in the range of $91900-95600 cm^{-1}$ via a single rovibrational level of $\bar{A}^{1}A_{u}$ as the intermediate. The prominent spectral features were due to trans-bending vibration progression ($V^{+}_{4}, K^{+}=0.3$) of the $X^{2}\Pi_{u}$ state of $C_{2}H^{+}_{2}$. Although transitions to levels of the is-bending vibration and levels with combination of $\nu^{+}_{2}, \nu^{+}_{4}$ and $\nu^{+}_{5}$ vibrational excitation were generally much weaker, the combination levels of (0,0,0,1,1) were fairly detected. From the parities and symmetrics of the nuclear spin of the observed rovibrational levels of the cations and the intermediate, we deduced that both odd and even partial waves were given off in the pulsed-field photoionization of the $\bar{A}$ state of acetylene. The spectroscopic parameters such as the trans-bending/cis-bending vibrational frequencies, anharmonicity constants, the gK corrections, and Renner-Teller parameters obtained from the best fit to the observed vibronic levels using a model for the Renner-Teller effect of molecule with two bending vibrational modes will be presented