Experimental Study of the NaK 31Π State

Abstract We report the results of an optical–optical double resonance experiment to determine the NaK 3 1 Π 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 Σ + ( v ′, J ′) ← 1( X ) 1 Σ + ( v ", J ") transition, and its frequency is then fixed. A second narrowband tunable cw Ti:Sapphirelaser (PROBE) is then scanned, while 3 1 Π → 1( X ) 1 Σ + violet fluorescence is monitored. The Doppler-free signals accurately map the 3 1 Π( v , J ) ro-vibrational energy levels. These energy levels are then fit to a Dunham expansion to provide a set of molecular constants. The Dunham constants, in turn, are used to construct an RKR potential curve. Resolved 3 1 Π( v , J ) → 1( X ) 1 Σ + ( v ", J ") fluorescence scans are also recorded with both PUMP and PROBE laser frequencies fixed. Comparison between observed and calculated Franck–Condon factors is used to determine the absolute vibrational numbering of the 3 1 Π state levels and to determine the variation of the 3 1 Π → 1( X ) 1 Σ + transitiondipole moment with internuclear separation. The recent theoretical calculation of the NaK 3 1 Π state potential reported by Magnier and Millie (1996, Phys. Rev. A 54, 204) is in excellent agreement with the present experimental RKR curve.