Direct measurement of a pure rotation transition in H-2(+)

The N = 1 <-- 0 pure rotation transition in the v = 19 level of the ground electronic state of H-2(+) was observed at 14961.7 +/- 1.1 MHz. Recent theo ry predicts significant electric dipole intensity in forbidden rotation and rotation-vibration transitions involving levels near the dissociation limi t; the relevant levels are bound by only 0.74 and 0.22 cm(-1). The transiti on was predicted to have a transition moment of 0.42 D: our measurement is consistent with this value.