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

A high-resolution infrared spectroscopic investigation of the halogen atom-HCN entrance channel complexes solvated in superfluid helium droplets

Rotationally resolved infrared spectra are reported for the X-HCN (X = Cl, Br, I) binary complexes solvated in helium nanodroplets. These results are directly compared with that obtained previously for the corresponding X-HF complexes [J. M. Merritt, J. K\"upper, and R. E. Miller, PCCP, 7, 67 (2005)]. For bromine and iodine atoms complexed with HCN, two linear structures are observed and assigned to the $^{2}\Sigma_{1/2}$ and $^{2}\Pi_{3/2}$ ground electronic states of the nitrogen and hydrogen bound geometries, respectively. Experiments for HCN + chlorine atoms give rise to only a single band which is attributed to the nitrogen bound isomer. That the hydrogen bound isomer is not stabilized is rationalized in terms of a lowering of the isomerization barrier by spin-orbit coupling. Theoretical calculations with and without spin-orbit coupling have also been performed and are compared with our experimental results. The possibility of stabilizing high-energy structures containing multiple radicals is discussed, motivated by preliminary spectroscopic evidence for the di-radical Br-HCCCN-Br complex. Spectra for the corresponding molecular halogen HCN-X$_{2}$ complexes are also presented.Comment: 20 pages, 15 figures, 6 tables, RevTe

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

Heat Treatment Procedure Qualification for Steel Castings

Heat treatment practices used by steel foundries have been carefully studied as part of comprehensive heat treatment procedure qualification development trials. These studies highlight the relationships between critical heat treatment process control parameters and heat treatment success. Foundry heat treatment trials to develop heat treatment procedure qualifications have shed light on the relationship between heat treatment theory and current practices. Furnace load time-temperature profiles in steel foundries exhibit significant differences depending on heat treatment equipment, furnace loading practice, and furnace maintenance. Time-temperature profiles of furnace control thermocouples can be very different from the time-temperature profiles observed at the center of casting loads in the furnace. Typical austenitization temperatures and holding times used by steel foundries far exceed what is required for transformation to austenite. Quenching and hardenability concepts were also investigated. Heat treatment procedure qualification (HTPQ) schema to demonstrate heat treatment success and to pre-qualify other alloys and section sizes requiring lesser hardenability have been developed. Tempering success is dependent on both tempering time and temperature. As such, furnace temperature uniformity and control of furnace loading during tempering is critical to obtain the desired mechanical properties. The ramp-up time in the furnace prior to the establishment of steady state heat treatment conditions contributes to the extent of heat treatment performed. This influence of ramp-up to temperature during tempering has been quantified