Characterization of gas-phase actinide

A multi-faceted spectroscopic approach will be utilize to precisely determine ground and excited state properties of small, gas-phase, uranium and thorium containing neutral molecules. In addition to being relevant to high temperature chemical environments (e.g. plasmas), these transient, refractory, gas-phase actinide containing molecules serve as the most direct link to a molecular-level theoretical understanding of actinide chemistry. The initial target molecules include ThX2, UX2 (X=C,O,F), ThCp and UCp. Supersonic molecular beam samples of the proposed molecules will be generated using an existing laser ablation/reaction source. The determined properties include vibronic state energies, bond lengths and angles, vibrational frequencies, permanent electric dipole moments, , magnetic dipole moments, , magnetic hyperfine interactions, radiative lifetimes, and oscillator strengths. The and values will be derived from the analysis of the spectral shifts and splittings induced by the application of either an external static electric (i.e. Stark effect) or magnetic (i.e. Zeeman effect) field. gives insight into the polarity of a chemical bond, and into the number of unpaired electrons. A comparison of our precisely determined molecular properties with predicted properties, particularly those for and , is the most effective means for assessing the methodologies being implemented (e.g. relativistic effective core potentials and four component wavefunction methods) for treating relativistic and electron correlation effects via Density Functional Theory (DFT) and Wave-Function Theory (WFT). Our laboratory has the unique ability to determine and for this class of molecules. Initial detection, production optimization, vibronic state energies determination, and oscillator strength determinations will be performed using a two dimensional (Excitation/Fluorescence) technique. In our version of this multiplexing approach, laser induced fluorescence (LIF) is imaged on the entrance slit of a monochromator equipped with a gated, intensified, CCD array. An approximate 75 nm wide spectral window of the dispersed fluorescence (DF) is monitored at a given angle setting of the grating of the monochromator. Great sensitivity is gained by the ability to gate out background emission and to simultaneously detect LIF at multiple wavelengths. Subsequently, near natural linewidth limit optical spectroscopy will be performed using single frequency lasers and a well collimated molecular beam. The field-free spectra will be analyzed to determine bond lengths and angles. The splittings resulting from interaction with non-zero nuclear spins (i.e. hyperfine splitting) will be used to assess the electronic state character. Subsequently, the optical spectra will be re-recorded and analyzed in the presence of static electric and magnetic fields to produce and . Ground state properties will be very precisely determined using the method of separated field, pump/probe microwave optical double resonance (PPMODR). In this scheme the microwave induced rotational, or other types of fine structure, transition are monitored as an increase in the probe beam LIF signal. PPMODR has the required molecular specificity and sensitivity due to optical detection. The wide operating frequency range of our PPMODR spectrometer (10-110 GHz) and the long exposure time of the molecules to the microwave field will be exploited to measure both electric dipole allowed pure transitions and much weaker magnetic dipole allowed transitions.