Laboratory measurements of small silicon bearing molecules of astrophysical interest

We will discuss the status of millimeter-wave laboratory measurements of the rotational spectra in the ground and vibrationally excited levels of small molecules containing two or three silicon atoms that might be the building blocks of dust seeds in carbon- and oxygen-rich AGB stars. The motivation is to provide essential spectroscopic information needed to guide future interferometric observations of the inner envelope of these objects at high angular resolution and sensitivity. The focus will be on a half-dozen species for which there is either no prior high resolution spectroscopy, or only in the centimeter band at best. We will also update the status of the known silicon carbides SiCC and SiCSi

Vibrational Satellites of C2_2S, C3_3S, and C4_4S: Microwave Spectral Taxonomy as a Stepping Stone to the Millimeter-Wave Band

We present a microwave spectral taxonomy study of several hydrocarbon/CS$_2$ discharge mixtures in which more than 60 distinct chemical species, their more abundant isotopic species, and/or their vibrationally excited states were detected using chirped-pulse and cavity Fourier-transform microwave spectroscopies. Taken together, in excess of 85 unique variants were detected, including several new isotopic species and more than 25 new vibrationally excited states of C$_2$S, C$_3$S, and C$_4$S, which have been assigned on the basis of published vibration-rotation interaction constants for C$_3$S, or newly calculated ones for C$_2$S and C$_4$S. On the basis of these precise, low-frequency measurements, several vibrationally exited states of C$_2$S and C$_3$S were subsequently identified in archival millimeter-wave data in the 253--280 GHz frequency range, ultimately providing highly accurate catalogs for astronomical searches. As part of this work, formation pathways of the two smaller carbon-sulfur chains were investigated using $^{13}$C isotopic spectroscopy, as was their vibrational excitation. The present study illustrates the utility of microwave spectral taxonomy as a tool for complex mixture analysis, and as a powerful and convenient `stepping stone' to higher frequency measurements in the millimeter and submillimeter bands.Comment: Accepted in PCC

NEW LABORATORY MEASUREMENTS OF RHOMBOIDAL SiC3_3

A.~J.~Apponi, M.~C.~McCarthy, C.~A.~Gottlieb, and P.~Thaddeus, {\sl Journ. Chem. Phys.A.~J.~Apponi, M.~C.~McCarthy, C.~A.~Gottlieb, and P.~Thaddeus, {\sl Astrophys. Journ. Lett.N.~A.~Patel, K.~H.~Young, S.~Brunken, R.~W.~Wilson, P.~Thaddeus, K.~M.~Menten, M.~Reid, M.~C.~McCarthy, Dinh-V~Trung, C.~A.~Gottlieb, and A.~Hedden, {\sl Astrophys. Journ.Author Institution: Harvard-Smithsonian Center for Astrophysics 60 Garden St. Cambridge, MA 02138; and School of Engineering \& Applied Sciences, Harvard University, 29 Oxford St.,Cambridge, MA 02138Rhomboidal SiC$_3$, the highly polar planar ring with C$_{2v}$ symmetry and a transannular C---C bond, was detected in our laboratory about 10~years ago, {\bf 111}, 3911 (1999).} and soon afterwards was identified with a radio telescope in the expanding envelope of IRC+10216. {\bf 516}, L103 (1999).} Recently a sensitive spectral line survey of IRC+10216 was made with the Submillimeter Array (SMA) in the $300 - 355$~GHz range with a $3^{\prime\prime} \times 2^{\prime\prime}$ synthesized beam. Many new lines were detected in this survey. Most are from high rotational transitions of molecules that are known in IRC+10216, but some of the lines are quite narrow and more than 10 of these are unassigned.nken, R.~W.~Wilson, P.~Thaddeus, K.~M.~Menten, M.~Reid, M.~C.~McCarthy, Dinh-V~Trung, C.~A.~Gottlieb, and A.~Hedden, {\sl Astrophys. Journ.}, in press (2009).} In support of the SMA observations we have extended the earlier laboratory measurements by Apponi {\it et al.} from 286~GHz and $K_a \le 6$, to 450~GHz and $K_a \le 20$ from rotational levels as high as 825~K above ground. As a result uncertainties in the predicted spectrum for lines with high $K_a$ have been reduced by as much as two orders of magnitude, which should aid the assignment of SiC$_3$ in the SMA survey and in future observations with ALMA. % ##########################################################################################

A Laboratory Study of C_3H^+ and the C_3H Radical in Three New Vibrationally Excited ^2Σ States Using a Pin-Hole Nozzle Discharge Source

Rotational lines of the positive molecular ion C_3H^+ and of the neutral C_3H radical in three new vibrationally excited states with ^2Σ symmetry have been detected in a supersonic molecular beam in the centimeter-wave band. The fundamental rotational line of the ion is quite weak, but is observed with similar intensity in a dc discharge through several different hydrocarbon gases when helium is the buffer gas. Under these conditions, the fractional abundance of C_3H^+ relative to C_3H is estimated to be of order 10^(−4), i.e., toward the lower end of the ratio (10^(−3)–10^(−4)) found for protonated ions using the same discharge nozzle. For each new ^2Σ state of the C_3H radical, spectroscopic constants, including those describing hydrogen hyperfine structure, have been determined to high precision. Lines of one ^2Σ state (B = 11271 MHz) are particularly intense in our molecular beam; for this state and a second one (B = 11306 MHz), millimeter-wave transitions have also been observed between 180 and 340 GHz using a long path dc glow absorption spectrometer. On the basis of intensity measurements with this spectrometer, the inferred rotation–vibration constant α, and theoretical calculations, the state with B = 11271 MHz is tentatively assigned to the ν_5 bending mode, predicted to lie ~300 cm^(−1) above ground

ROTATIONAL SPECTRA OF THE MOLECULAR IONS H2_2NCO+^+ AND NCO−^-

Author Institution: Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, and School of Engineering and Applied Science, Harvard University, Cambridge, MA 02138; Max-Planck-Institut fur Radioastronomie, Bonn, Germany, and I. Physikalisches Institut, Universitat zu Koln, GermanyWe report the first high resolution spectroscopic detection of H$_2$NCO$^+$, the protonated cation of isocyanic acid, in a discharge through HNCO heavily diluted in hydrogen in the throat of a supersonic nozzle. Spectroscopic constants derived from the two lowest rotational transitions agree very well with theoretical structure calculations of the ground state isomer, in which protonation occurs at the nitrogen atom, yielding an isomer of C$_{2v}$ symmetry. In the same molecular beam, the fundamental rotational transition of NCO$^-$ was observed with well-resolved nitrogen quadrupole hyperfine structure. Detection of NCO$^-$ in our beam was subsequently confirmed by observation of several millimeter-wave transitions in a low pressure discharge through cyanogen and water. The spectroscopic constants of NCO$^-$ obtained earlier by infrared laser spectroscopy nderline{\textbf{86}}, 6631, (1987).} are in good agreement with the highly accurate constants derived here. Owing to the high abundance of HNCO in many galactic molecular sources, both ions are excellent candidates for astronomical detection in the radio band. %The rotational spectrum of H$_2$NCO$^+$ has been recently detected in a supersonic molecular beam. through the discharge of isocyanic acid heavily diluted in a hydrogen expansion. Under the same experimental conditions, the fundamental rotational transition of NCO$^-$ has also been observed, showing the expected hyperfine structure from the presence of the nitrogen nucleus. The laboratory search has been guided by high level quantum chemical calculations and the rotational constant derived by infrared laser spectroscopy nderline{\textbf{86}}(12), 6631 June 1987.} for the anion. Due to the high abundance of HNCO in several interstellar medium regions, these two molecular ions represent serious candidates for detection through radio-astronomical techniques. %By means of high resolution microwave techniques, the spectra of NCO$^-$ and H$_2$NCO$^+$ has been recently detected. The laboratory search of the cation has been guided by theoretical structure calculations performed at the CCSD(T)/cc-pwCVQZ level of theory corrected for zero-point vibrational effects at the CCSD(T)/cc-pVQZ level. The anion search has been based on the rotational constant derived by infrared laser spectroscopy nderline{\textbf{86}}(12), 6631 June 1987.} and the nitrogen quadrupole coupling constant calculated at the CCSD(T)/aug-cc-pwCVQZ level of theory. Both species have produced using isocyanic acid heavily diluted in a hydrogen expansion. The spectrum of both ions shows expected hyperfine structure from the presence of the nitrogen nucleus, providing a crucial confirmation of the discovery. Due to the large and ubiquitous presence of isocyanic acid in several interstellar medium regions, these two molecular ions represent serious candidates for detection through radio-astronomical techniques

Submillimeter narrow emission lines from the inner envelope of IRC+10216

A spectral-line survey of IRC+10216 in the 345 GHz band has been undertaken with the Submillimeter Array. Although not yet completed, it has already yielded a fairly large sample of narrow molecular emission lines with line-widths indicating expansion velocities of ~4 km/s, less than 3 times the well-known value of the terminal expansion velocity (14.5 km/s) of the outer envelope. Five of these narrow lines have now been identified as rotational transitions in vibrationally excited states of previously detected molecules: the v=1, J=17--16 and J=19--18 lines of Si34S and 29SiS and the v=2, J=7--6 line of CS. Maps of these lines show that the emission is confined to a region within ~60 AU of the star, indicating that the narrow-line emission is probing the region of dust-formation where the stellar wind is still being accelerated.Comment: 5 pages, 5 figures, Accepted for publication in Ap

Determinants and Impact of Giardia Infection in the First 2 Years of Life in the MAL-ED Birth Cohort

Background. Giardia are among the most common enteropathogens detected in children in low-resource settings. We describe here the epidemiology of infection with Giardia in the first 2 years of life in the Etiology, Risk Factors, and Interactions of Enteric Infections and Malnutrition and the Consequences for Child Health and Development Project (MAL-ED), a multisite birth-cohort stu dy. Methods. From 2089 children, 34 916 stool samples collected during monthly surveillance and episodes of diarrhea were tested for Giardia using an enzyme immunoassay. We quantified the risk of Giardia detection, identified risk factors, and assessed the associations with micronutrients, markers of gut inflammation and permeability, diarrhea, and growth using multivariable linear regression. Results. The incidence of at least 1 Giardia detection varied according to site (range, 37.7%–96.4%) and was higher in the sec - ond year of life. Exclusive breastfeeding (HR for first Giardia detection in a monthly surveillance stool sample, 0.46 [95% confidence interval (CI), 0.28–0.75]), higher socioeconomic status (HR, 0.74 [95% CI, 0.56–0.97]), and recent metronidazole treatment (risk ratio for any surveillance stool detection, 0.69 [95% CI, 0.56–0.84]) were protective. Persistence of Giardia (consecutive detections) in the first 6 months of life was associated with reduced subsequent diarrheal rates in Naushahro Feroze, Pakistan but not at any other site. Giardia detection was also associated with an increased lactulose/mannitol ratio. Persistence of Giardia before 6 months of age was associated with a −0.29 (95% CI, −0.53 to −0.05) deficit in weight-for-age z score and −0.29 (95% CI, −0.64 to 0.07) deficit in length-for-age z score at 2 years. Conclusions. Infection with Giardia occurred across epidemiological contexts, and repeated detections in 40% of the children suggest that persistent infections were common. Early persistent infection with Giardia , independent of diarrhea, might contribute to intestinal permeability and stunted growth

Nuggets, Pearls, and Vignettes of Master Heart Failure Clinicians

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73696/1/j.1527-5299.2001.00307.x.pd