Generation and High‐Resolution Photoelectron Spectroscopy of Small Organic Radicals in Cold Supersonic Expansions

A general method of generating radicals in cold supersonic expansions in the gas phase is presented. The method relies on excimer laser photolysis of suitable precursor molecules in a thin quartz capillary mounted at the orifice of a pulsed gas nozzle and can easily be combined with vacuum‐UV photoionization mass spectrometry and high‐resolution photoelectron spectroscopy to study the reactivity and the rovibronic energy level structure of neutral radicals and their ions, as well as to determine highly accurate adiabatic ionization energies. The characteristics of the radical source are described in detail, and its performance is illustrated by mass spectrometric and high‐resolution photoelectron spectroscopic investigations of NH 2 , CH 2 , CH 3 , C 2 H, C 2 H 3 , and C 2 H 5 . The radical source is not only suitable to produce cold samples (rotational temperature of ca. 30 K) of radicals of moderate reactivity, such as NH 2 , CH 3 , or C 2 H 5 , but it is also useful to prepare highly reactive radicals ( e.g. , C 2 H) for spectroscopic investigations.