Microwave spectra of van der Waals complexes of importance in planetary atmospheres

The Fourier-transform Fabry-Perot pulsed-molecular-beam microwave spectrometer at NIST was used to study the microwave spectra of a number of molecular dimers and trimers that may be present in planetary atmospheres. The weak van der Waals bonds associated with these species usually give rise to rotational-tunneling splittings in the microwave spectra. The microwave spectrum of the water dimer species was used to illustrate the complications that can arise in the study of the rotational spectra of these loosely bound species. In addition to the water dimer species, the microwave spectra of the following hydrogen-bonded and van der Waals complexes were studied: (CO2)2-H2O, CO2-(H2O)2, CO2-H2S, N2-H2O, CO-H2O, SO2-H2O, and O3-H2O

The Effect of Two Commercially Available Beverages on Fluid Retention During Exercise in Heat

Occupational athletes such as wildland firefighters (WLFF) endure extreme conditions leading to high levels of fluid loss. While performing wildfire suppression, it is vital to maintain hydration in order to sustain exercise in high temperatures. PURPOSE: The purpose of this study was to compare two commercially available beverages (DD [60.9 mM Na+, 3.4% CHO] vs G [18.4 mM Na+, 5.9% CHO]) on hydration maintenance during submaximal exercise in the heat. METHODS: Ten aerobically fit males (22.5± 3.9 yrs, 82.2± 10.1 kg, 53.9± 5.9 ml•kg-1•min-1 VO2 Max) completed two 90-minute heat stress trials (39º C, 30% RH) working at 50% VO2 max followed by a 30-minute rest period in a heat chamber. Forty-five minutes into each trial, 150% of sweat rate was replaced with a randomly ordered beverage (G or DD). Subjects wore standard WLFF Nomex uniforms. Rating of perceived exertion (RPE) and heart rate (HR) were recorded every fifteen minutes. Blood samples were obtained pre- and post-exercise and post-trial to measure changes in hemoglobin (mg•dL-1) and plasma volume (%). Sweat rate was calculated by change in nude body weight. Data was analyzed using analysis of variance (ANOVA). RESULTS: There was a significant effect of time on HR following exercise (142.5 ± 6.3 at 15 min, vs 175.4 ± 4.7 b•min-1 at 90 min; p\u3c0.001). RPE was significantly lower in G than DD at 15 and 30 minutes following exercise (8.0 ± 0.6 and 6.7 ± 0.3 vs 10.4 ± 1.1 and 8.1 ± 0.8; for G and DD respectively; TrtXTime p=0.015). Additionally, hemoglobin was significantly affected by time (15. 8 ± 0.4 vs 16.3 ± 0.4 g•dL-1 post-trial; p\u3c0.01). Plasma volume, USG, and urine volume (mL) were not different (p=0.4, p=0.8, p=0.5 respectively) between trials. Sweat rate and percent dehydration from mid to post trial were not different (p=0.9, p=0.8 respectively) between beverages. CONCLUSION: Neither beverage (DD [60.9mmol/L Na+, 3.4% CHO] vs G [18.4mmol/L Na+, 5.9% CHO]) differed in fluid retention following exercise in the heat, however RPE was attenuated in G vs. DD. This study was supported by the US Forest Service

Spectroscopic parameters for silacyclopropynylidene, SiC2_2, from extensive astronomical observations toward CW Leo (IRC +10216) with the Herschel satellite

A molecular line survey has been carried out toward the carbon-rich asymptotic giant branch star CW Leo employing the HIFI instrument on board of the Herschel satellite. Numerous features from 480 GHz to beyond 1100 GHz could be assigned unambiguously to the fairly floppy SiC$_2$ molecule. However, predictions from laboratory data exhibited large deviations from the observed frequencies even after some lower frequency data from this survey were incorporated into a fit. Therefore, we present a combined fit of all available laboratory data together with data from radio-astronomical observations.Comment: 7 pages, 1 figure, J. Mol. Spectrosc., appeared; CDMS links corrected (version 2; current version: 3; may be updated later this year

Microwave rotation-tunneling spectroscopy of the water–methanol dimer: Direct structural proof for the strongest bound conformation

Rotation-tunneling a-type spectra of CH3OH[centered ellipsis]H2O and CH3OD[centered ellipsis]D2O were recorded between 18 and 60 GHz using direct absorption microwave spectroscopy, and for CH3OH[centered ellipsis]H2O, 13CH3OH[centered ellipsis]H2O, CH3OH[centered ellipsis]DOH, CD3OH[centered ellipsis]H2O, and CH3OD[centered ellipsis]D2O between 7 and 24 GHz using a Fourier-transform microwave spectrometer. Because CH3OH and H2O are capable of both accepting and donating hydrogen bonds, there exists some question as to which donor–acceptor pairing of the molecules is the lowest energy form. This question is further emphasized by the ambiguity and variety present in previous experimental and computational results. Transitions arising from the methyl torsional A state were assigned in each of the studied isotopomers, and for the A and E states in CH3OH[centered ellipsis]H2O. While the measured components of the dipole moment for the parent (H,12C,16O) isotopomer—µa = 7.956 ± 0.03 × 10^–30 C m (2.385 ± 0.008 D), µb = 3.636 ± 0.02 × 10^–30 C m (1.090 ± 0.006 D), µc = 0.43 ± 0.47 × 10^–30 C m (0.13 ± 0.14 D), where the errors correspond to 1 sigma uncertainties—are consistent with either conformation, the fit of the structure to the rotational constants demonstrates unambiguously that the lower-energy conformation formed in supersonically cooled molecular beams corresponds to a water–donor, methanol–acceptor complex. The results and implications for future work are also discussed in terms of the permutation-inversion theory presented by Hougen and Ohashi [J. Mol. Spectros. 159, 363 (1993)]

Manipulating the motion of large neutral molecules

Large molecules have complex potential-energy surfaces with many local minima. They exhibit multiple stereo-isomers, even at very low temperatures. In this paper we discuss the different approaches for the manipulation of the motion of large and complex molecules, like amino acids or peptides, and the prospects of state- and conformer-selected, focused, and slow beams of such molecules for studying their molecular properties and for fundamental physics studies. Accepted for publication in Faraday Disc. 142 (2009), DOI: 10.1039/b820045aComment: 12 page

A line confusion limited millimeter survey of Orion KL (I): sulfur carbon chains

We perform a sensitive (line confusion limited), single-side band spectral survey towards Orion KL with the IRAM 30m telescope, covering the following frequency ranges: 80-115.5 GHz, 130-178 GHz, and 197-281 GHz. We detect more than 14 400 spectral features of which 10 040 have been identified up to date and attributed to 43 different molecules, including 148 isotopologues and lines from vibrationally excited states. In this paper, we focus on the study of OCS, HCS+, H2CS, CS, CCS, C3S, and their isotopologues. In addition, we map the OCS J=18-17 line and complete complementary observations of several OCS lines at selected positions around Orion IRc2 (the position selected for the survey). We report the first detection of OCS v2 = 1 and v3 = 1 vibrationally excited states in space and the first detection of C3S in warm clouds. Most of CCS, and almost all C3S, line emission arises from the hot core indicating an enhancement of their abundances in warm and dense gas. Column densities and isotopic ratios have been calculated using a large velocity gradient (LVG) excitation and radiative transfer code (for the low density gas components) and a local thermal equilibrium (LTE) code (appropriate for the warm and dense hot core component), which takes into account the different cloud components known to exist towards Orion KL, the extended ridge, compact ridge, plateau, and hot core. The vibrational temperature derived from OCS v2 = 1 and v3 = 1 levels is about 210 K, similar to the gas kinetic temperature in the hot core. These OCS high energy levels are probably pumped by absorption of IR dust photons. We derive an upper limit to the OC3S, H2CCS, HNCS, HOCS+, and NCS column densities. Finally, we discuss the D/H abundance ratio and infer the following isotopic abundances: 12C/13C=45+-20, 32S/34S=20+-6, 32S/33S=75+-29, and 16O/18O=250+-135.Comment: Accepted for publication in A&

A line confusion limited millimeter survey of Orion KL. II: Silicon-bearing species

We present a study of the Silicon-bearing species detected in a line confusion limited survey towards Orion KL performed with the IRAM 30-m telescope, which ranges from 80 to 280 GHz. Our aim is to derive physical and chemical conditions for each family taking into account all observed lines from all isotopologues of each species. We have modeled the lines of the detected molecules using a radiative transfer code, which permit us to choose between LVG and LTE approximations depending on the physical conditions of the gas. We have used appropriate collisional rates for the LVG calculations. For the v=1 state of SiO we have detected the J=2-1 line and, for the first time in this source, emission in the J=4-3 transition, both of them showing strong masering effect. For SiO v=0, we have detected 28SiO, 29SiO, and 30SiO; in addition, we have mapped the J = 5-4 SiO line. For SiS, we have detected the main species, 29SiS, and SiS v=1. Unlikely other species detected in Orion KL (IRc2), the emission peak of SiS appears at a velocity of ~15.5 km s-1; a study of the 5-4 SiO line around IRc2 shows this feature as an extended component that probably arises from the interaction of the outflow with the ambient cloud. We derive a SiO/SiS column density ratio of ~13 in the plateau component. Besides, we provide upper limits to the column density of several non-detected Silicon-bearing species. The results of our chemical models show that while it is possible to reproduce SiO in the gas phase (as well as on the grains), SiS is a product of surface reactions, most likely involving direct reactions of S with Si.Comment: Astronomy and Astrophysics, in pres

An atomic and molecular database for analysis of submillimetre line observations

Atomic and molecular data for the transitions of a number of astrophysically interesting species are summarized, including energy levels, statistical weights, Einstein A-coefficients and collisional rate coefficients. Available collisional data from quantum chemical calculations and experiments are extrapolated to higher energies. These data, which are made publically available through the WWW at http://www.strw.leidenuniv.nl/~moldata, are essential input for non-LTE line radiative transfer programs. An online version of a computer program for performing statistical equilibrium calculations is also made available as part of the database. Comparisons of calculated emission lines using different sets of collisional rate coefficients are presented. This database should form an important tool in analyzing observations from current and future (sub)millimetre and infrared telescopes.Comment: Accepted for publication in A&A, 14 pages, 5 figure

The microwave spectrum, structure and dipole moment of 1,4-pentadiyne

The microwave spectra of 1,4-pentadiyne and 1,4-pentadiyne-1,5-d2 are assigned and rotational and centrifugal distortion constants obtained. A unique structure could not be determined. However, analysis of the moments of inertia indicates that the bond distances in C5H4 are close to typical values found in other related compounds. An interaction involving the acetylene moieties is evidenced by the derived bond angles. The data are consistent with either the central CCC angle being close to the tetrahedral value with the acetylene groups pushed away from linearity by approximately 3-4[deg] or opening of the central CCC angle to about 113[deg] along with linear acetylene groups. A range of structures between these two is also possible. The dipole moment is determined to be 0.516(5) D.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24440/1/0000713.pd