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. Increasing or decreasing the rate of this process creates branches respectively named for the French words riche and pauvre. A gas’ partition function contains a term equal to “k T over (*) B” representing the contribution of this process. (-5[1])The energy of this process in a (10[1])diatomic molecule is proportional to j times j plus one in an idealized “rigid” model. Microwave spectroscopy observes modes corresponding to this process that couple to vibrational modes and experience centrifugal distortion. For 10 points, name this process that gives a molecule nonzero angular momentum. ■END■ (10[2])