THE A(2)SIGMA(-CENTER-DOT-NO STUDIED USING RESONANCE-ENHANCED MULTIPHOTON AND ZERO-KINETIC-ENERGY PULSED-FIELD IONIZATION SPECTROSCOPY() STATE OF AR)

Resonance-enhanced multiphoton ionization (REMPI) and zero-kinetic-ene rgy pulsed-field ionization (ZEKE-PFI) techniques have been used to st udy the spectroscopy of the (A) over tilde (2) Sigma(+) Ar . No.<(A)ov er tilde (2) Sigma(+)> - (X) over tilde (II)-I-2 REMPI spectra of Ar . NO have been interpreted using two different models that have allowed assignment of the observed rovibronic transitions to be made and an e stimate of the strength of the (A) over tilde state intermolecular pot ential to be determined. Simulations of the spectra have indicated tha t the ground vibrationless level of the (A) over tilde state has a lin ear geometry while some higher vibrational levels have a skewed T-shap ed structure. The analysis has also confirmed that the (A) over tilde state of Ar . NO is very weakly bound and is non-Rydberg in character. Reported for the first time are ZEKE-PFI spectra observed via the int ermediate <(A)over tilde (2) Sigma(+)> state. No structure was detecte d close to the ionization threshold, although peaks observed at higher elicitation energy have been assigned to transitions to high-lying vi brational levels of the Ar . NO+ ion. ZEKE-PFI spectra recorded via th e ground vibrational level of the intermediate (A) over tilde state, w hich has a linear structure, show progressions which correlate with tr ansitions to highly excited van der Waals stretching and bending level s; however, spectra recorded via an intermediate level with a T-shaped geometry show progressions which correlate principally with the van d er Waals stretching mode. These assignments have been interpreted in t erms of the large changes in intermolecular bond length and bond angle upon ionization and fully support the interpretation of the REMPI spe ctra. The results of the REMPI and ZEKE-PFI spectra have also been use d to investigate the character of the (A) over tilde state and the geo metry that the complex adopts in each of the vibronic levels of this s tate has been rationalized in terms of the possible interactions invol ved. (C) 1998 American Institute of Physics.