Abstract

Optical-optical double resonance spectroscopy of molecules with high fluorescence quantum yield (e.g., Na₂) has usually been carried out by fluorescence detection. However, we have found that a space-charge-limited diode ionization detector provides a significant sensitivity enhancement for excited states of Na₂ that can associatively ionize $\left({\text{Na}}_2+\text{Na}\to {\text{Na}}_3^{+}+e^{-}\right)$. These are excited states with electronic energies of ≥228,000 cm^-1. For example, we recently studied the $4^1{\Sigma }_g^{+}$ “shelf”¹ and the ¹2Π_g states² of Na₂ by using fluorescent detection observing υ ≤ 127 and υ≤ 43, respectively. These levels correspond to 83% and 80% of the potential well depth and have outer RKR turning points of 13.4 and 6.5 Å, respectively. Using our new ionization detector, we have observed levels υ ≤ 177 and υ ≤ 79, respectively. These levels correspond to 99% and 99% of the potential well depth and have preliminary outer RKR turning points of 17.0 and 18.1 Å, respectively.

© 1992 Optical Society of America