Spectroscopy of pendular states: The use of molecular complexes in achieving orientation

Infrared-laser--molecular-beam spectroscopy has been used to observe strongly bound pendular states of the linear hydrogen cyanide trimer. The spectrum undergoes a dramatic evolution from that of a free rotor at zero electric field, with its characteristic P and R branch structure, to that indicative of a pendulum bound by a large electric field (corresponding to =/B=365). The result is an unprecedented degree of orientation for a linear molecule. The generality of using weakly bound complexes to orient even nonpolar molecules is discussed.