First measurement of the rotational constants for the homonuclear molecular ion He-2(+)

The velocity of the dissociative recombination final product state atoms ha s been used to measure the rotational constants B-upsilon and D-upsilon of the upsilon = 3 level in He-2(+). The energy of the upsilon = 3 level in He -2(+) has also been measured and from this measurement, along with existing spectroscopic constants, the binding energy D-0(0) of He-2(+) has been det ermined. We find D-0(0) = 2.4457 +/- 0.0002 eV, B-upsilon = 6.46 +/- 0.2 cm (-1), and D-upsilon = -7.1 x 10(-4) +/- 0.0003 cm(-1). These measurements d emonstrate a new method of measurement of some molecular constants that has accuracies comparable to optical spectroscopy.