Experimental study of the NaK 3(1)Pi state

We report the results of an optical-optical double resonance experiment to determine the NaK 3(1)II state potential energy curve. In the first step, a narrow band cw dye laser (PUMP) is tuned to line center of a particular 2( A)(1)Sigma(+)(v', J') <-- 1(X)(1)Sigma(+)(v ", J ") transition, and its fre quency is then fixed. A second narrowband tunable cw Ti:Sapphirelaser (PROB E) is then scanned, while 3(1)II --> 1(X)(1)Sigma(+) violet fluorescence is monitored. The Doppler-free signals accurately map the 3(1)II(v, J) re-vib rational energy levels. These energy levels are then fit to a Dunham expans ion to provide a set of molecular constants. The Dunham constants, in turn, are used to construct an RKR potential curve. Resolved 3(1)II(v, J) --> 1( X)(1)Sigma(+)(v ", J ") fluorescence scans are also recorded with both PUMP and PROBE laser frequencies fixed. Comparison between observed and calcula ted Franck-Condon factors is used to determine the absolute vibrational num bering of the 3(1)II state levels and to determine the variation of the 3(1 )II --> 1(X)(1)Sigma(+) transition-dipole moment with internuclear separati on. The recent theoretical calculation of the NaK 3(1)II state potential re ported by Magnier and Millie (1996, Phys. Rev. A 54, 204) is in excellent a greement with the present experimental RKR curve. (C) 1999 Academic Press.