Hughes and Wilson increased the sensitivity of an instrument detecting this process by applying a high voltage square wave in the first use of Stark modulation. The partition function of this process can be solved by using the Euler–Maclaurin formula and dividing by a symmetry factor sigma. (15[1])Increasing or decreasing the rate of this process creates branches respectively named for the French (-5[1])words riche and pauvre. A gas’ partition function contains (15[1])a term equal to “k T over (*) B” representing the contribution of this process. The energy of this process in a diatomic molecule (10[1])is proportional to j times (10[1])j plus one in an idealized “rigid” model. Microwave spectroscopy observes modes corresponding to this process (-5[1])that couple to vibrational (10[1])modes and experience centrifugal distortion. For 10 points, name this process that gives a molecule nonzero angular momentum. ■END■ (10[1])