Infrared Observations During the Secondary Eclipse of HD 209458b: I. 3.6-Micron Occultation Spectroscopy Using the VLT

We search for an infrared signature of the transiting extrasolar planet HD 209458b during secondary eclipse. Our method, which we call `occultation spectroscopy,' searches for the disappearance and reappearance of weak spectral features due to the exoplanet as it passes behind the star and later reappears. We argue that at the longest infrared wavelengths, this technique becomes preferable to conventional `transit spectroscopy'. We observed the system in the wing of the strong nu-3 band of methane near 3.6 microns during two secondary eclipses, using the VLT/ISAAC spectrometer at a spectral resolution of 3300. Our analysis, which utilizes a model template spectrum, achieves sufficient precision to expect detection of the spectral structure predicted by an irradiated, low-opacity (cloudless), low-albedo, thermochemical equilibrium model for the exoplanet atmosphere. However, our observations show no evidence for the presence of this spectrum from the exoplanet, with the statistical significance of the non-detection depending on the timing of the secondary eclipse, which depends on the assumed value for the orbital eccentricity. Our results reject certain specific models of the atmosphere of HD 209458b as inconsistent with our observations at the 3-sigma level, given assumptions about the stellar and planetary parameters.Comment: 26 pages, 8 figures Accepted to Astrophysical Journa

Tunable far infrared laser spectroscopy of a ternary van der Waals cluster Ar2HCl: A sensitive probe of three-body forces

The first far infrared intermolecular vibration—rotation spectrum of the ternary van der Waals cluster has been measured near 39.5 cm-1 and assigned to an a-type [Sum] bending vibration of Ar2HCl. Spectra of both chlorine isotopes were observed and nuclear quadrupole hyperfine structure was resolved. Values of the fitted constants (rotational constants, hyperfine projections) evidence large amplitude out-of-plane motion, and demonstrate the sensitivity of spectroscopic observables to the three body forces operative in the Ar2HCl system. Spectroscopic predictions calculated by Hutson et al. from pairwise-additive and ‘‘three-body’’ corrected potential energy surfaces [J. Chem. Phys. 90, 1337 (1989)] are compared to experimental results

Far-infrared laser vibration—rotation—tunneling spectroscopy of the propane—water complex: Torsional dynamics of the hydrogen bond

The far-infrared laser vibration—rotation—tunneling (FIR-VRT) spectrum of the propane—water complex has been measured in the range 18—22 cm-1. A C-type VRT band has been assigned with a band origin of 19.6 cm-1. The data support the ‘‘kite-shaped’’ structure determined from microwave spectroscopy in the accompanying paper, and indicate that the observed VRT band corresponds to torsional motion of the free water proton about the hydrogen bond. This motion is impeded by a barrier that is less than 5 cm-1. We describe our modification of the supersonic slit-jet source designed to permit Stark effects to be measured, and have used second-order Stark shifts to help assign the perpendicular transition observed

An investigation of three-body effects in intermolecular forces II: Far-infrared vibration—rotation—tunneling laser spectroscopy of Ar2HCl

A second Ar2HCl intermolecular vibration—rotation band centered at 37.2 cm-1 has been measured and assigned as a b-type transition originating from the ground state. Nuclear hyperfine splittings were resolved for both chlorine isotopes. The rotational constants determined from the data indicate coupling between an Ar—Ar stretching or bending coordinate and the Ar2 —HCl vibrational coordinates. As a result of this particular vibrational motion, Ar2H 35Cl undergoes an axis-switching transition while the Ar2H 37Cl isotope does not. In addition, the measured hyperfine projections indicate the possibility of coupling between the Ar2 —HCl stretching and bending modes, preventing an absolute vibrational assignment. These results indicate that the ‘‘reversed adiabatic’’ approximation employed by Hutson, Beswick, and Halberstadt in their theoretical study of Ar2HCl [J. Chem. Phys. 90, 1337 (1989)] is not appropriate for the complicated intramolecular dynamics presently observed in this system

Far-infrared vibration-rotation-tunnelling spectroscopy of ArDCl: A critical test of the H6(4, 3, 0) potential surface

Three intermolecular vibrations of the ArDCl complex have been observed by tunable far-infrared laser spectroscopy in a supersonic planar jet. Vibration-rotation-tunnelling transitions to states correlating to the j = 1, Θ = 0, the j = 2, Θ = 0, and the j = 2, Θ = 1 internal rotor levels of DCl have been measured for both chlorine isotopes with nuclear quadrupole hyperfine resolution. The fitted spectroscopic constants are compared with recent calculations from the new H6(4, 3, 0) ArHCl potential by Hutson and it is concluded that, although the new potential is very accurate, significant discrepancies between observed and calculated values exist for states which probe the secondary minimum (ArClH) of the potential

Fourier transform microwave spectrum of the propane—water complex: A prototypical water-hydrophobe system

The Fourier transform microwave spectrum of the propane—water complex (C3H8—H2O) has been observed and analyzed. This spectrum includes transitions assigned to propane complexed with both the ortho and para nuclear spin confirmations of water. The rotational constants indicate that the vibrationally averaged structure has all four heavy atoms coplanar, with the water center of mass lying on or near the C2 axis of propane, inside the CCC angle, 3.76(±0.02) A-ring from the propane center-of-mass, and 4.35(±0.02) A-ring from the methylene carbon. The projection of the electric dipole onto the a inertial axis of the complex (0.732 D for the ortho state and 0.819 D for the para state) indicates that one of the protons of the water subunit lies on the C2 axis of the propane monomer, which is also the axis connecting the subunit centers of mass. The small projection of the dipole along the b axis (0.14 D for the ortho state and 0.38 D for the para state) is most consistent with an equilibrium structure in which all three atoms of the water lie in the CCC plane of propane, with torsional tunneling about the hydrogen bond occurring on the same time scale as the overall rotation. The small internal rotation tunneling splittings that occur in the rotational spectrum of the propane monomer are not observed in the spectrum of the complex

Comparative genomics and stx phage characterization of LEE-negative Shiga toxin-producing Escherichia coli

Infection by Escherichia coli and Shigella species are among the leading causes of death due to diarrheal disease in the world. Shiga toxin producing Escherichia coli (STEC) that do not encode the locus of enterocyte effacement (LEE-negative STEC) often possess Shiga toxin gene variants and have been isolated from humans and a variety of animal sources. In this study, we compare the genomes of nine LEE-negative STEC harboring various stx alleles with four complete reference LEE-positive STEC isolates. Compared to a representative collection of prototype E. coli and Shigella isolates representing each of the pathotypes, the whole genome phylogeny demonstrated that these isolates are diverse. Whole genome comparative analysis of the 13 genomes revealed that in addition to the absence of the LEE pathogenicity island, phage encoded genes including non-LEE encoded effectors, were absent from all nine LEE-negative STEC genomes. Several plasmid-encoded virulence factors reportedly identified in LEE-negative STEC isolates were identified in only a subset of the nine LEE-negative isolates further confirming the diversity of this group. In combination with whole genome analysis, we characterized the lambdoid phages harboring the various stx alleles and determined their genomic insertion sites. Although the integrase gene sequence corresponded with genomic location, it was not correlated with stx variant, further highlighting the mosaic nature of these phages. The transcription of these phages in different genomic backgrounds was examined. Expression of the Shiga toxin genes, stx1 and/or stx2, as well as the Q genes, were examined with quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) assays. A wide range of basal and induced toxin induction was observed. Overall, this is a first significant foray into the genome space of this unexplored group of emerging and divergent pathogens

Terahertz vibration-rotation-tunneling spectroscopy of the propane–water dimer: The ortho-state of a 20cm^(−1) torsion

We report the detailed characterization of a torsional vibration-rotation-tunneling band of the ortho-state of the propane–water dimer in the spectral region near 20 cm^(−1) (0.6 THz). This work extends the previously reported studies with more than one hundred new transitions included in a combined fit with the 155 previously reported transitions in both the microwave and terahertz regions for this torsional band. More than six hundred transitions have now been recorded in the interval 500 and 810 GHz