Chemical applications of zero kinetic energy (ZEKE) photoelectron spectroscopy

ZEKE spectroscopy is a new method in chemical spectroscopy which particularly addresses ionic species by measuring (ro)vibronic states of the ion through detection of isoenergetic, stable Rydberg states. These states are extremely long-lived and can therefore be measured with high precision. The new spectroscopy allows very high resolution measurements of positively charged ions. This approach can be extended to photodetachment of anions, producing information about the corresponding neutral molecule. ZEKE spectroscopy has already been applied to a wide variety of molecular ions, clusters, van der Waals molecules, free radicals, reactive intermediates, and even to elusive transition states of chemical reactions. Compared to conventional photoelectron spectroscopy, ZEKE spectroscopy offers many advantages, for example, greatly increased spectral resolution. This allows one to obtain the rotational structure of large molecular cations such as the benzene cation and the intermolecular vibrations of molecular clusters such as phenol-water.