The extension of IR cryo-SEVI to polyatomic molecules presents several challenges. First, although many infrared spectra of negative ions have been obtained through "tagging" experiments, it is still the case that relatively few vibrational frequencies are known for gas phase anions. Secondly, at the fewcm -1 resolution of the cryo-SEVI instrument, one does not expect to resolve individual rotational transitions in polyatomic anions. Finally, the vibrational state excited by the IR laser may be anharmonically coupled to nearby vibrational levels, leading to more complexity in the resulting photoelectron spectrum than implied by the simple picture in Figure .