Chemistry, Spectroscopy And Isotope Separation Of Zirconium And Its Compounds As Revealed By Laser Diagnostics Of Laser Produced Metal Beams.

Invited PaperChemistry, spectroscopy and isotope separation of zirconium and its compounds as revealed bylaser diagnostics of laser produced metal beams.Peter A. Hackett, Mark Humphries, David M. Rayner, Orson L. Bourne and Steven A. MitchellDivision of ChemistryNational Research CouncilOttawa, Ontario, CanadaK1A OR6AbstractRecent work from our laboratory on zirconium beams is reviewed. Zirconium metal beamshave been produced by laser vaporization of solid zirconium targets coupled with supersonicexpansion of helium gas. The resultant supersonic metal beam is shown to present an idealenvironment for various spectroscopic techniques. The state distribution of zirconium atomsin the beam is obtained from low resolution laser induced fluorescence (LIF) studies. Highresolution LIP studies give information on the hyperfine splitting in the ground state ofthe zirconium -91 isotope. Information on the hyperfine splitting in the excited state isobtained from quantum beat spectroscopy. Low resolution 2 color multiphoton ionizationspectroscopy using a XeC1 laser allows isotope separation of all isotopes of zirconium.This same technique, using a tunable UV laser reveals that the previously accepted valuesfor the ionization potential for zirconium are in chemically significant error (2500 cm -1)and permits precise ( ±0.3 cm -1) measurement of the ionization potential for this element viathe observation of long (n =55 to 80) Rydberg series.These metal beams are highly reactive and can be used to produce novel chemicalspecies. The results of two studies in which a reactant is added to the expansion gas arereported here. Zirconium oxide (ZrO), a molecule observed in the emission spectra of coolstars and in laboratory studies at high temperatures, is produced in a low temperature,collision free environment by adding small quantities of oxygen to the expansion gas.Zirconium fluoride (ZrF), a molecule previously unobserved, is produced by the addition ofsmall quantities of CF4.IntroductionSmalley and co- workers at Rice University have introduced techniques which have allowedprofound advances in the areas of the chemistry, structure and spectroscopy of moleculesderived from refractory materials. At the core of these advances are two, dramaticallynon -equilibrium, processes: laser vaporization and supersonic expansion. By the former weare able to vaporize even the most refractory of materials using modest amounts of laserenergy as a result of the combination of extremely rapid heating and extremely smallinteraction volumes inherent in the technique. By the latter we are able to convert a highpressure gas in which all degrees of freedom are in dynamic equilibrium into a low pressure,"collisionless" gas in which all degrees of freedom are frozen at values which arecharacteristic of the form and rate of the expansion. Smalley and co- workers combined thesetechniques by placing the refractory material at the high pressure region of a pulsed, raregas expansion and ensuring that the gas and laser pulses were synchronous. This simple beamsource has been used in numerous studies of the chemistry and spectroscopy of dimers,trimers and clusters of refractory elements culminating in the strikingly beautifuldemonstration gf2the stability of huckminsterfullerene (C60) in both neutral and negativelycharged forms.