The multiphoton ionization of uranium hexafluoride

Thesis/Dissertation · Wed Jan 01 04:00:00 EST 1992

OSTI ID:7072255

Armstrong, D P

Multiphoton ionization (MPI) time-of-flight mass spectroscopy and photoelectron spectroscopy studies of UF[sub 6] have been conducted using focused light from the Nd:YAG laser fundamental ([lambda] = 1064 nm) and its harmonics ([lambda] = 532, 355, or 266 nm), as well as other wavelengths provided by a tunable dye laser. The MPI mass spectra are dominated by the singly and multiply charged uranium ions rather than by the UF[sub x][sup +] fragment ions. The laser power dependence of U[sup n+] ion signals indicates that saturation can occur for many of the steps required for their ionization. The doubly-charged uranium ion (U[sup 2+]) intensity is much greater than that of the singly-charged uranium ion (U[sup +]). For the case of the tunable dye laser experiments, the U[sup n+] (n=1-4) wavelength dependence is relatively unstructured and does not show observable resonance enhancement at known atomic uranium excitation wavelengths. The dominance of the U[sup 2+] ion and the absence or very small intensities of UF[sub x][sup +] fragments, along with the unstructured wavelength dependence, indicate that mechanisms may exist other than ionization of bare U atoms after the stepwise photodissociation of F atoms from the parent molecule. The data argue against step-wise photodissociation of UF[sub x][sup +] (x = 5,6) ions. Neither the neutral ladder nor the ion ladder mechanisms adequately describe the ionization phenomena observed. These results suggest an alternate mechanism which better explains the multiphoton excitation and dissociative ionization of UF[sub 6]. It is likely that the multiphoton excitation of UF[sub 6] under these experimental conditions results in a superexcited molecule, UF[sub 6][sup **], which primarily dissociates into U[sup n+] (through multiple channels), fluorine atoms, and slow electrons. The excitation of such superexcited molecules may be facilitated by the existence of a previously reported giant resonance at 12-14 eV.

• Research Organization: Tennessee Univ., Knoxville, TN (United States)
• OSTI ID: 7072255
• Country of Publication: United States
• Language: English

Related Subjects

664200* -- Spectra of Atoms & Molecules & their Interactions with Photons-- (1992-)
74 ATOMIC AND MOLECULAR PHYSICS
ACTINIDE COMPOUNDS
ELECTROMAGNETIC RADIATION
ELECTRON SPECTROSCOPY
FLUORIDES
FLUORINE COMPOUNDS
HALIDES
HALOGEN COMPOUNDS
IONIZATION
LASER RADIATION
MASS SPECTRA
MULTI-PHOTON PROCESSES
PHOTOELECTRON SPECTROSCOPY
PHOTOIONIZATION
RADIATIONS
SPECTRA
SPECTROSCOPY
URANIUM COMPOUNDS
URANIUM FLUORIDES
URANIUM HEXAFLUORIDE