We present Submillimeter Wave Astronomy Satellite (SWAS) observations of the
1_{10}-1_{01} transition of ortho-water at 557 GHz toward 12 molecular cloud
cores. The water emission was detected in NGC 7538, Rho Oph A, NGC 2024, CRL
2591, W3, W3(OH), Mon R2, and W33, and was not detected in TMC-1, L134N, and
B335. We also present a small map of the water emission in S140. Observations
of the H_2^{18}O line were obtained toward S140 and NGC 7538, but no emission
was detected. The abundance of ortho-water relative to H_2 in the giant
molecular cloud cores was found to vary between 6x10^{-10} and 1x10^{-8}. Five
of the cloud cores in our sample have previous water detections; however, in
all cases the emission is thought to arise from hot cores with small angular
extents. The water abundance estimated for the hot core gas is at least 100
times larger than in the gas probed by SWAS. The most stringent upper limit on
the ortho-water abundance in dark clouds is provided in TMC-1, where the
3-sigma upper limit on the ortho-water fractional abundance is 7x10^{-8}.Comment: 5 pages, 3 Postscript figures, uses aastex.cls, emulateapj5.sty
(included), and apjfonts.sty (included
New extensive millimeter-wave measurements of the 12 C 16 O dimer have been made, and more than 300 new spectral transitions have been observed in the frequency range 81-135 GHz. A joint analysis of these and previous millimeter-wave data yielded the precise location of 33 new energy levels of A + symmetry and 20 levels of A -symmetry. These energy levels are located at 8-18 cm -1 above the zero-point level. Some of them belong to already known stacks, and others make up 9 new stacks of the dimer. Newly determined stacks have K ) 0, 1, and, for the first time, 2, where K is the projection of the total angular momentum on the intermolecular axis. The energy levels from accompanying rovibrational calculations with the use of a recently developed hybrid CCSD(T)/DFT-SAPT potential are in very good agreement with experiment. Analysis of the calculated wave functions revealed that two new stacks of A + symmetry with K ) 2 correspond to overall rotation of the dimer while the other newly observed stacks belong to the geared bend overtone modes. The ground vibrational states of the two "isomers" found are more or less localized at the two minima in the potential surface, whereas all the geared bend excited states show a considerable amount of delocalization.
Gas-phase oxadisulfane (HSOH), the missing link between the well-known molecules hydrogen peroxide (HOOH) and disulfane (HSSH), was synthesized by flash vacuum pyrolysis of di-tert-butyl sulfoxide. Using mass spectrometry, the pyrolysis conditions have been optimized towards formation of HSOH. Microwave spectroscopic investigation of the pyrolysis products allowed-assisted by high-level quantum-chemical calculations--the first measurement of the rotational-torsional spectrum of HSOH. In total, we have measured approximately 600 lines of the rotational-torsional spectrum in the frequency range from 64 GHz to 1.9 THz and assigned some 470 of these to the rotational-torsional spectrum of HSOH in its ground torsional state. Some 120 out of the 600 lines arise from the isotopomer H(34)SOH. The HSOH molecule displays strong c-type and somewhat weaker b-type transitions, indicating a nonplanar skew chain structure, similar to the analogous molecules HOOH and HSSH. The rotational constants (MHz) of the main isotopomer (A=202 069, B=15 282, C=14 840), determined by applying a least-squares analysis to the presently available data set, are in excellent agreement with those predicted by quantum-chemical calculations (A=202 136, B=15 279, C=14 840). Our theoretical treatment also derived the following barrier heights against internal rotation in HSOH (when in the cis and trans configurations) to be V(cis) approximately equal to 2216 cm(-1) and V(trans) approximately equal to 1579 cm(-1). The internal rotational motion results in detectable torsional splittings that are dependent on the angular momentum quantum numbers J and K(a).
We report the first extragalactic detection of the neutral carbon [CI] 3 P 2 → 3 P 1 fine structure line at 809 GHz. The line was observed towards M 82 simultaneously with the 3 P 1 → 3 P 0 line at 492 GHz, providing a precise measurement of the J = 2 → 1/J = 1 → 0 integrated line ratio of 0.96 (on a [K km s −1 ]-scale). This ratio constrains the [CI] emitting gas to have a temperature of at least 50 K and a density of at least 10 4 cm −3 . Already at this minimum temperature and density, the beam averaged CI-column density is large, 2.1 10 18 cm −2 , confirming the high CI/CO abundance ratio of ≈ 0.5 estimated earlier from the 492 GHz line alone. We argue that the [CI] emission from M 82 most likely arises in clouds of linear size around a few pc with a density of about 10 4 cm −3 or slightly higher and temperatures of 50 K up to about 100 K.
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