Delroy A. Baugh

Production of a pure, single ro-vibrational quantum-state molecular beam

Abstract Electrostatic hexapole focusing is used to produce a beam of ND3 molecules in a pure, single |JKMϵ〉|±〉≡|1111〉|−〉 rational—vibrational quantum state in the electronic ground state, X , 1A′1. Both photodissociation at 193.3 nm and (2+1) REMPI are used to detect the state-selected ND3 molecules. Calculated focusing curves are shown to be in good agreement with the experimental curves for initial beam temperatures less than 6 K and special simulations confirm the single state nature of the molecular beam by comparisons to the measured population and alignment (A[2]O=0.5±0.1) of the focused |1111〉|−〉 state.

Extraction of the transition dipole matrix from the photodissociation of oriented/aligned parent molecules

A formalism for the analysis of detailed photofragmentation experiments involving oriented/aligned parent molecules is presented. It is demonstrated for the photofragmentation of an oriented/aligned parent molecule that both the magnitudes and the relative‐phases of the transition dipole matrix elements can be determined from angle integrated cross sections or the product orientation/alignment moments derived from them. Formulas are presented for extracting transition dipole matrix elements from the photodissociation of an aligned diatomic molecule to form aligned and/or oriented atomic products using linearly or circularly polarized photolysis lasers. While these detailed measurements are ideally performed using inhomogeneous field state‐selected parent molecules, they can be also readily carried out by doing double‐resonance photodissociation experiments with polarized lasers. The analysis presented here can, therefore, be used to extract the transition dipole matrix elements from these double‐resonance...

Determination of transition dipole matrix elements for the 266 nm photofragmentation of ∣JKM〉 state-selected CD3I

Abstract The photofragmentation of rovibrational energy-level and magnetic-state polarized ( X 1 A 1 )CD 3 I ∣JKM〉≡∣111〉 was performed at 266 nm. The ∣ NK ) rotational energy level distribution and the angular momentum polarization of the vibrationless ( X 2 A″ 2 ) CD 3 photofragment were measured by (2+1) REMPI. State-selecting the parent CD 3 I allowed the elements of the transition dipole matrix (or T -matrix) to be determined by relating the initial system (CD 3 I plus photon) statistical tensors to measured product statistical moments. This is believed to be the first report of the experimental determination of T -matrix elements for a chemical reaction.

Experimental and theoretical photofragmentation dynamics of rovibronic-magnetic state-selected ND3

Results of experimental and theoretical studies of the rovibrationally state-selected photodissociation dynamics of ND 3 at 193.3 nm are reported. ND 3 molecules in the antisymmetric inversion doublet level were state-selectively focused, using an electrostatic hexapole, into several rovibronic-magnetic states. The velocity distributions of the D atom for photofragmentation of ND 3 in each of these fully selected states were measured using Doppler spectroscopy. The resulting Doppler profiles were fitted by comparison with profiles calculated using a fully quantum mechanical photofragmentation theory. At the high photon energies considered, the total photofragmentation cross-section was found to be relatively insensitive to the initial rotational energy level. Analysis of the fully state-selected differential photofragmentation cross-sections in terms of R-, Q- and P-branch scattering waves allowed the matrix elements of the transition dipole operator to be determined. These matrix elements confirm a parallel transition with the D atom recoiling primarily along the C 3 axis for the photodissociation of ND 3 at 193.3 nm.

Structure and dynamics from polarized parent/product photofragmentation spectroscopy

Energy-level selected nitrosyl chloride (ClNO) was rotationally polarized (aligned/oriented) and photodissociated at 355 nm. Polarization sensitive detection of the NO(2Π) product was used to measure the magnitudes and relative phases of the transition amplitudes (T-matrix elements) for the coherent excitation of continuum wavefunctions representing the dissociating molecule on the excited potential energy surface. Rotational state-populations were also measured and a smaller number of ∣NΩ) levels were found to be occupied than in non-state-selected, jet-cooled experiments. The theoretical formalism necessary for the extraction of the T-matrix elements from fully polarized experiments is also presented. Finally, hexapole focusing curves demonstrate excellent ∣JK) energy-level selection for the parent ClNO and the NO(2Π) photofragment angular distribution demonstrates for the first time dipole orientation and rotational alignment, i.e., ∣M∣ selection, of a state-selected asymmetric top by an electrostatic hexapole.

Rotational state-selective photofragmentation of ND3 at 193.3 nm

Highly resolved JKM> state-selected beams of ND3 were produced and the experimentally determined hexapole focusing curves are in good agreement with simulated curves calculated with the ND3 temperature as the only adjustable parameter. ND3 molecules in the 111> state were photodissociated at 193.3 nm and the angular and kinetic energy distributions of the resulting D-atoms were measured by velocity-aligned Doppler spectroscopy.

Conductivity and gating of silicon ringchains

One-dimensional and two-dimensional conductivity calculations are done for a set of several closely spaced quantum silicon rings, following the development of bottom-up approaches for producing silicon rings. The transmission is easily influenced by electric and magnetic gatings and has band features even for two or three rings, showing its potential usefulness for logical devices. Analysis on different gatings shows that the electric-field gating would be as effective as the Aharonov-Bohm magnetic gating.

Ultra-short time resolution from energy-dependent interference of photodissociation amplitudes

Abstract Measuring the wavelength dependence of photodissociation transition amplitudes to crossing electronic states is discussed with reference to extracting time domain information. Outwards from the crossing the system evolves on one or the other state as ascertained from the electronic state of the products. One can therefore measure the phase difference for the motion on the two potentials accumulated between the Franck–Condon region and the crossing point. A computational example, the photodissociation of HI and DI, is provided. The interference varies rapidly with wavelength and provides considerable leverage for determination of ultra-short time differences. The interference exhibits a significant isotope effect.

Virtual angular momentum: The dynamics of inverting molecules in an electrostatic hexapole field

The semiclassical dynamics of a molecule which undergoes tunneling inversion while traversing an electrostatic hexapole field is shown to be described by the motion of a two dimensional harmonic oscillator with angular momentum Lv. Analytical expressions are provided which show explicitly the dependence of Lv on the molecular inversion frequency. A comparison between calculated and experimental focusing curves is also presented.