The G 1Πg state of Li27 revisited: Observation and analysis of high vibrational levels

CW optical–optical double resonance has been employed to study the upper portion of the G 1Πg state of Li27. The use of fluorescence and ion detection enabled the observation of vibrational levels ranging from v=20 to 48 and rotational levels ranging from J=1 to 25. For optical–optical double resonance experiments the Franck–Condon factors between these levels and useful A 1Σu+ state levels (levels that can be reached from the thermally populated levels of the ground state) were exceedingly small. The sensitive ionization detection made possible observation of this upper, anharmonic region of the potential. From the data a Rydberg–Klein–Rees potential curve was constructed which represents over 99% of the potential well depth. A C5 coefficient has been calculated and represents the first experimental determination of a long range coefficient for a doubly excited state in diatomic lithium.