Low noise tunnel diode receivers for satellite application

Low noise tunnel diode receivers for satellite application

Candidate molecular ions for an electron electric dipole moment experiment

This paper is a theoretical work in support of a newly proposed experiment (R. Stutz and E. Cornell, Bull. Am. Soc. Phys. 89, 76 2004) that promises greater sensitivity to measurements of the electron's electric dipole moment (EDM) based on the trapping of molecular ions. Such an experiment requires the choice of a suitable molecule that is both experimentally feasible and possesses an expectation of a reasonable EDM signal. We find that the molecular ions PtH+, HfH+, and HfF+ are suitable candidates in their low-lying triplet Delta states. In particular, we anticipate that the effective electric fields generated inside these molecules are approximately of 73 GV/cm, -17 GV/cm, and -18 GV/cm respectively. As a byproduct of this discussion, we also explain how to make estimates of the size of the effective electric field acting in a molecule, using commercially available, nonrelativistic molecular structure software.Comment: 25 pages, 3 figures, submitted to Physical Review

Rotational Feshbach Resonances in Ultracold Molecular Collisions

In collisions at ultralow temperatures, molecules will possess Feshbach resonances, foreign to ultracold atoms, whose virtual excited states consist of rotations of the molecules. We estimate the mean spacing and mean widths of these resonant states, exploiting the fact the molecular collisions at low energy display chaotic motion. As examples, we consider the experimentally relevant molecules O_2, OH, and PbO. The density of s-wave resonant states for these species is quite high, implying that a large number of narrow resonant states will exist.Comment: 4 pages, 2 figure

UNDERSTANDING CH5+_5^+ SPECTROSCOPY FROM A PARTICLE-ON-A-SPHERE MODEL

Author Institution: JILA, Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309Due to the low barrier to H rearrangement in CH$_5^+$, a good approximation is to separate the angular and radial H coordinates. By fixing R$_{CH}$ at a constant value, the 15 degree-of-freedom problem becomes a more computationally feasible 10 degree-of-freedom problem. The reduced dimensional problem is well suited for capturing the essential low energy, large amplitude bending/rotation dynamics. The "particle-on-a-sphere" (POS) model, which has been shown to provide good experimental agreement in XH$_n$ (n=2-4) systems is extended to accommodate a 5 hydrogen system. Building on past success with the XH$_n$ systems, we use the XH$_5$ POS model to calculate the patterns of the low J rovibrational spectrum, facilitating the understanding of the jet-cooled CH$_5^+$ spectrum

PARTICLES-ON-A-SPHERE: A REDUCED DIMENSIONAL APPROACH TO LARGE-AMPLITUDE MOTION FOR POLYATOMIC HYDRIDES

Author Institution: JILA, Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309We introduce a relatively simple but computationally tractable "particle-on-a-sphere" (POS) model for the intramolecular motion of light atoms constrained to the surface of a sphere. The model assumes independent 2D angular motion of H atoms embedded on the surface of a sphere with an arbitrary interatomic angular potential, which permits systematic evolution from "free rotor" to "tunneling" to "quasi-rigid" polyatomic molecule behavior for small values of total angular momentum J. This work focuses on the simple tetratom (n=3) system as a function of interatomic potential stiffness, with explicit consideration of H$_3$O$^+$ as a test case. The particle-on-a-sphere model also establishes the necessary mathematical groundwork for calculations on dynamically much more challenging XH$_n$ species with n$>$3, (e.g., reduced dimensional models of CH$_5^+$), where such an approach offers prospects for being quantum mechanically tractable at low J values characteristic of supersonic jet expansion conditions

Large-amplitude quantum mechanics in polyatomic hydrides II A particle-on-a-sphere model for XHn (n=4,5)

This paper describes the application of a relatively simple, but computationally tractable, “particle-on-a-sphere” (POS) model for quantum-mechanical calculation of large-amplitude, H atom dynamics in polyatomic hydrides (XHn), based on radially relaxed, two-dimensional angular motion of H atoms on the surface of a sphere. This work focuses on systems with many degrees of freedom, i.e., XH4 (eight dimensional) and XH5 (ten dimensional), with corresponding molecular analogs of CH4 and CH5+ and is applicable to rovibrationally excited states with J ≥ 0. A pairwise-additive potential fit for CH5+, which yields remarkable agreement with geometries, energies, and barrier heights on the full-dimensional surface of Brown et al. [J. Chem. Phys. 121, 4105 (2004)] is presented. Comparisons with experimental data and diffusion quantum Monte Carlo (DMC) methods test convergence for the POS model and provide insight into multidimensional quantum rovibrational dynamics. In particular, POS energy-level patterns for a series of scaled CH5+ potentials indicate an absence of strong tunneling behavior, consistent with the highly delocalized wave functions, large zero-point energies, and small interconversion barriers noted in previous DMC studies of Brown et al