Double-resonance spectroscopy of a complex resonance in molecular nitrogen.

Abstract

Double-resonance spectroscopy via several rotational levels of the ${\mathrm{N}}_{2}$ ${\mathit{a}}^{1}$${\mathrm{\ensuremath{\Pi}}}_{\mathit{g}}$, v'=5 state has been used to probe the rotational structure of a complex autoionizing resonance observed just below the ${\mathit{X}}^{2}$${\mathrm{\ensuremath{\Sigma}}}_{\mathit{g}}^{+}$, ${\mathit{v}}^{+}$=1 threshold. A multichannel-quantum-defect-theory (MQDT) analysis confirms that the complex resonance is produced by the interaction of two interloping states with the np and nf Rydberg series converging to the ${\mathit{X}}^{2}$${\mathrm{\ensuremath{\Sigma}}}_{\mathit{g}}^{+}$, ${\mathit{v}}^{+}$=1 limit. The quantum defects of the interlopers and their interaction strengths with the two Rydberg series are determined from fits of the MQDT model to the energies of the peaks observed in the complex resonance. The experimentally determined interaction parameters and those available from ab initio calculations are in fair agreement. The present results complete the interpretation of the photoionization spectrum of ${\mathrm{N}}_{2}$ in the energy region between the ${\mathit{X}}^{2}$${\mathrm{\ensuremath{\Sigma}}}_{\mathit{g}}^{+}$, ${\mathit{v}}^{+}$=0 and 1 thresholds.