Observation of a shape resonance in the athinsp3 summation u+ state of 7Li2

Using the most accurate potential curves available for the athinsp3 summation u+ and Xthinsp1 summation g+ states of lithium molecules, we compute the positions of shape resonances. We also calculate the deexcitation probability from a bound level v' with rotational number N' to the continuum of the lower state, and conclude that a shape resonance should be measurable for the transition 2thinsp3 product g→athinsp3 summation u+. Such a shape resonance has been identified from the spectra of the transition from the v'=2,N'=4 level of 2thinsp3 product g into the Ndouble-prime=4 continuum of athinsp3 summation u+. Its position is in good agreement with the theoretical prediction. copyright 1999 The American Physical Society