Photoelectron spectra in intense laser fields: The effect of resonance with autoionizing Rydberg states

The effect of autoionizing Rydberg states on photoelectron spectra in intense laser fields were studied. On the basis of the multichannel quantum defect theory combined with the artificial channel method, the spectral structures caused by the s-Rydberg series converging on ${\mathrm{CO}}^{+}{(X}^{2}{\ensuremath{\Sigma}}^{+},v=1)$ were calculated. It is found that the shape of spectra remarkably changes depending on the laser intensity. The spectra for higher Rydberg states undergo the change by a weaker laser field, reflecting sensitivity of a weakly bound Rydberg electron. A kind of n-scaling law for this sensitivity is discussed.