2-COLOR DOUBLE-RESONANCE SPECTROSCOPY VIA (A)TILDE 1AU STATE OF ACETYLENE - 3P-RYDBERG STATE AND ITS RENNER-TELLER EFFECT

The two-color double resonance multiphoton ionization spectra due to the transitions from various rovibrational levels of the A approximately 1 A(u) state of acetylene to the 3p Rydberg state have been measured. The observed spectra showed large dependence on the quantum number K. It was concluded from the spectral analysis that the geometry of the 3p Rydberg state is linear. The spectra also showed a long progression of the trans-bending vibration, supporting the linear structure. The trans-bending progression belonging to the 1-DELTA(g) electronic state showed the Renner-Teller splittings. The observed splittings were reproduced by the calculation using the formulas for a linear triatomic molecule in a DELTA-electronic state.