P. A. Willis, H. U. Stauffer, R. Z. Hinrichs and H. F. Davis*

Department of Chemistry and Chemical Biology

Baker Laboratory

Cornell University

Ithaca NY 14853-1301

December, 1998

To be submitted to Review of Scientific Instruments

A newly constructed universal crossed molecular beams apparatus with fixed UHV quadrupole mass spectrometer detector and rotatable beam sources is described. Production of electronically cold neutral supersonic transition metal atom beams using laser vaporization is demonstrated. The beams are characterized by laser induced fluorescence spectroscopy, photodepletion spectroscopy, and time-of-flight analysis. Photoionization of reaction products using the pulsed 157 nm radiation from an F₂ excimer laser in the ionization region of the mass spectrometer is demonstrated for Zr + C₂H₄ -> ZrC₂H₂ + H₂. Compared to conventional electron impact ionization, 157 nm photoionization yields greatly improved signal-to-noise ratios and essentially zero background. countrate. Reactions of several hydrocarbons including ethane with the very weakly reactive Y atom is also presented. Due to the small reaction cross section, electron impact ionization was unfeasible for Y reactions, whereas VUV photoionization at 193 nm and 157 nm facilitated direct studies of both reactive and non-reactive collisions. We also demonstrate the use of 1+1 resonance enhanced multiphoton ionization for state selective detection of nonreactively scattered transition metal atoms from crossed beam reactions. The greatly improved sensitivity of the photoionization technique facilitates studies of transition metal systems not previously amenable to the crossed beams method.

*Author to whom correspondence should be addressed at HFD1@cornell.edu