Universal crossed molecular beams apparatus with synchrotron photoionization mass spectrometric product detection

Vacuum ultraviolet radiation was generated from an undulator at the Advanced Light Source Synchrotron facility and used for photoionization detection of reaction products in a new universal crossed molecular beams machine. A description of the machine and its performance is presented. Initial experiments on the photodissociation of methylamine (CH₃NH₂), ozone (O₃), oxalyl chloride [(OCCl)₂] as well as the reactive scattering of Cl with C₃H₈ show many of the advantages of photoionization in comparison to electron impact ionization, which has been exclusively used in such instruments in the past. "Momentum matching" of reaction products is much more easily accomplished than in electron impact studies due to suppression of dissociative ionization. The tunability of the vacuum ultraviolet radiation can be used to suppress background from residual gases especially when it is desired to detect free radical reaction products. Even when the tunability cannot be used to suppress background, the fact that little heat is generated by the ionizing beam allows background to be substantially suppressed by cryogenic pumping. The energy resolution of the apparatus is comparable to instruments that have previously been designed with electron impact ionization which have more than twice as long a flight path. This new instrument provides outstanding performance for fundamental studies of chemical dynamics.