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. The energy of this process in a diatomic molecule is proportional to j times j plus one in an idealized “rigid” model. Microwave spectroscopy observes modes corresponding (10[1])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. (10[1])■END■ (10[1])