Lineshapes of autoionizing molecular Rydberg states probed by laser-induced grating spectroscopy

Two-color laser-induced grating spectroscopy (TC-LIGS) of NO via the A {sup 2}{Sigma}, v{prime} = 0 and 1 state has been used to investigate several ns, np, and nf Rydberg states of NO. Transition energies and lineshapes obtained with this four-wave mixing technique are compared to those obtained by using multiphoton ionization detection. Rydberg series converging to the first ionization potential are observed up to n{approx}40; higher members of the Rydberg series are obscured by a continuum contribution to the LIGS signal. At low laser powers the linewidths of the observed autoionizing states obtained by using TC-LIGS are in agreement with data obtained from ionization studies. However, with higher laser powers, the lineshapes of the autoionizing states change dramatically.