The pure rotational spectrum of NaCN has been recorded in the millimeter/submillimeter region using direct absorption techniques, the first experimental study of this molecule at frequencies above 40 ...GHz. The species was produced in the gas phase in an AC discharge by the reaction of sodium vapor with cyanogen. Twelve rotational transitions of NaCN have been measured in the range of 180-530 GHz, extending the previous microwave data to millimeter/submillimeter frequencies. Multiple Ka asymmetry components were recorded in each rotational transition up to Ka = 5 or 6, a total of 131 individual lines. These data have been analyzed with a standard asymmetric top Hamiltonian, combined with prior microwave measurements. Higher-order centrifugal distortion terms were clearly needed to model the millimeter-wave transitions of this floppy molecule. From this revised set of spectroscopic constants, accurate frequency predictions can now be made up to 600 GHz for NaCN for the lower-value Ka components (Ka <= 4). Based on the new laboratory data and past spectral surveys, a revised abundance for NaCN in IRC+10216 has been estimated. For a 5'' source, the fractional abundance for this molecule was found to be f (NaCN/H2) ~ 1 X 10--8, comparable to that of c-C3H2. These new frequency measurements should aid in line identification in surveys in the 0.8 mm band and at shorter wavelengths.
The pure rotational spectrum of the ZnCCH (X̃(2)Σ(+)) radical has been measured using Fourier transform microwave (FTMW) and millimeter direct-absorption methods in the frequency range of 7-260 GHz. ...This work is the first study of ZnCCH by any type of spectroscopic technique. In the FTMW system, the radical was synthesized in a mixture of zinc vapor and 0.05% acetylene in argon, using a discharge assisted laser ablation source. In the millimeter-wave spectrometer, the molecule was created from the reaction of zinc vapor, produced in a Broida-type oven, with pure acetylene in a dc discharge. Thirteen rotational transitions were recorded for the main species, (64)ZnCCH, and between 4 and 10 for the (66)ZnCCH, (68)ZnCCH, (64)ZnCCD, and (64)Zn(13)C(13)CH isotopologues. The fine structure doublets were observed in all the data, and in the FTMW spectra, hydrogen, deuterium, and carbon-13 hyperfine splittings were resolved. The data have been analyzed with a (2)Σ Hamiltonian, and rotational, spin-rotation, and H, D, and (13)C hyperfine parameters have been established for this radical. From the rotational constants, an r(m) ((1)) structure was determined with r(Zn-C) = 1.9083 Å, r(C-C) = 1.2313 Å, and r(C-H) = 1.0508 Å. The geometry suggests that ZnCCH is primarily a covalent species with the zinc atom singly bonded to the C≡C-H moiety. This result is consistent with the hyperfine parameters, which suggest that the unpaired electron is localized on the zinc nucleus. The spin-rotation constant indicates that an excited (2)Π state may exist ∼19,000 cm(-1) in energy above the ground state.
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•First measurement of the rotational spectrum of a metal phosphide species.•Rotational and fine-structure constants accurately determined for CrP (X4Σ−)•Confirms CrP bond length of ...2.117 Å, ∼0.1 Å shorter than theoretical predictions.•Provides an experimental benchmark for theoretical studies of metal phosphides.•Novel synthesis technique used to generate phosphorus vapor.
The submillimeter spectrum of the CrP radical (X4Σ−) has been recorded using direct absorption techniques in the frequency range 347–545 GHz. This study is the first pure rotational measurement of a metal-phosphide species. CrP was synthesized in an AC discharge in argon by the reaction of gas-phase chromium with phosphorus vapor, produced by a novel source. Twelve rotational transitions of CrP were measured, each consisting of four fine structure components. The spectra were analyzed using a Hund’s case (b) Hamiltonian, and rotational, spin-spin, and spin-rotation constants determined. The 3d phosphides appear to resemble the corresponding nitrides in terms of bonding.
The NaCl molecule has been observed in the circumstellar envelopes of VY Canis Majoris (VY CMa) and IK Tauri (IK Tau)--the first identifications of a metal refractory in oxygen-rich shells of evolved ...stars. Five rotational transitions of NaCl at 1 and 2 mm were detected toward VY CMa and three 1 mm lines were observed toward IK Tau, using the telescopes of the Arizona Radio Observatory. In both objects, the line widths of the NaCl profiles were extremely narrow relative to those of other molecules, indicating that sodium chloride has not reached the terminal outflow velocity in either star, likely a result of early condensation onto grains. Modeling the observed spectra suggests abundances, relative to H sub(2), of f similar to 5 x 10 super(-9) in VY CMa and f similar to 4 x 10 super(-9) in IK Tau, with source sizes of 0.5" and 0.3", respectively. The extent of these sources is consistent with the size of the dust acceleration zones in both stars. NaCl therefore appears to be at least as abundant in O-rich shells as compared to C-rich envelopes, where f similar to (0.2-2) x 10 super(-9), although It appears to condense out earlier in the O-rich case. Chemical equilibrium calculations indicate that NaCl is the major carrier of sodium at T similar to 1100 K for oxygen-rich stars, with predicted fractional abundances in good agreement with the observations. These measurements suggest that crystalline salt may be an important condensate for sodium in both C- and O-rich circumstellar shells.
Observations of the carbon-bearing molecules CO, HCN, CS, HNC, CN, and HCO+ have been conducted toward the circumstellar envelope of the oxygen-rich red supergiant star, VY Canis Majoris (VY CMa), ...using the Arizona Radio Observatory (ARO). CO and HCN were also observed toward the O-rich shells of NML Cyg, TX Cam, IK Tau, and W Hya. Rotational transitions of these species at 1 mm, 0.8 mm, and 0.4 mm were measured with the ARO Submillimeter Telescope, including the J = 6 -> 5 line of CO at 691 GHz toward TX Cam and W Hya. The ARO 12 m was used for 2 mm and 3 mm observations. Four transitions were observed for HCO+ in VY CMa, the first definitive identification of this ion in a circumstellar envelope. Molecular line profiles from VY CMa are complex, indicating three separate outflows: a roughly spherical flow and separate red- and blueshifted winds, as suggested by earlier observations. Spectra from the other sources appear to trace a single outflow component. The line data were modeled with a radiative transfer code to establish molecular abundances relative to H2 and source distributions. Abundances for CO derived for these objects vary over an order of magnitude, f ~ 0.4-5 X 10-4, with the lower values corresponding to the supergiants. For HCN, a similar range in abundance is found (f ~ 0.9-9 X 10-6), with no obvious dependence on the mass-loss rate. In VY CMa, HCO+ is present in all three outflows with f ~ 0.4-1.6 X 10-8 and a spatial extent similar to that of CO. HNC is found only in the red- and blueshifted components with HCN/HNC ~ 150-190, while CN/HCN ~ 0.01 in the spherical flow. All three velocity components are traced in CS, which has a confined spatial distribution and f ~ 2-6 X 10-7. These observations suggest that carbon-bearing molecules in O-rich shells are produced by a combination of photospheric shocks and photochemistry. Shocks may play a more prominent role in the supergiants because of their macroturbulent velocities.
A sensitive (1{sigma} rms at 1 MHz resolution {approx}3 mK) 1 mm spectral line survey (214.5-285.5 GHz) of VY Canis Majoris (VY CMa) and IRC +10216 has been conducted to compare the chemistries of ...oxygen- and carbon-rich circumstellar envelopes. This study was carried out using the Submillimeter Telescope of the Arizona Radio Observatory with a new Atacama Large Millimeter Array type receiver. This survey is the first to chemically characterize an O-rich circumstellar shell at millimeter wavelengths. In VY CMa, 128 emission features were detected arising from 18 different molecules; and in IRC +10216, 720 lines were observed, assigned to 32 different species. The 1 mm spectrum of VY CMa is dominated by SO{sub 2} and SiS; in IRC +10216, C{sub 4}H and SiC{sub 2} are the most recurrent species. Ten molecules were common to both sources: CO, SiS, SiO, CS, CN, HCN, HNC, NaCl, PN, and HCO{sup +}. Sulfur plays an important role in VY CMa, but saturated/unsaturated carbon dominates the molecular content of IRC +10216, producing CH{sub 2}NH, for example. Although the molecular complexity of IRC +10216 is greater, VY CMa supports a unique 'inorganic' chemistry leading to the oxides PO, AlO, and AlOH. Only diatomic and triatomic compounds were observed in VY CMa, while species with four or more atoms are common in IRC +10216, reflecting carbon's ability to form multiple strong bonds, unlike oxygen. In VY CMa, a new water maser (v {sub 2} = 2) has been found, as well as vibrationally excited NaCl. Toward IRC +10216, vibrationally excited CCH was detected for the first time.
The N = 1 ← 0 transition of SH{sup +} (X{sup 3}Σ{sup −}) in its complete fine structure multiplet (J = 0 ← 1, 2 ← 1, and 1 ← 1) has been measured using submillimeter/THz direct absorption ...spectroscopy in the frequency range near 346–683 GHz. This work is the first direct laboratory measurement of the J = 0 ← 1 and 1 ← 1 spin components. This molecular ion was created in the gas phase from a mixture of H{sub 2}S and argon in an AC discharge. Hyperfine components, arising from the nuclear spin of H (I = 1/2), were resolved in every fine structure multiplet. The data have been analyzed using a Hund’s case b{sub βJ} Hamiltonian, resulting in further improvement in the accuracy of the rotational, spin–rotation, spin–spin, and magnetic hyperfine constants for SH{sup +}. From these new data, frequency predictions have been made for the N = 2 → 1 and 3 → 2 transitions, with an estimated uncertainty of less than 1 MHz. These data also confirm the recent detection of the two hyperfine components of the N = 1 → 0, J = 0 → 1 transition of SH{sup +} in the Orion Bar, as well as the J = 1 → 1 component of this molecular ion near 683 GHz toward Sgr B2.
We compare detailed observations of multiple H2O maser transitions around the red supergiant star VY CMa with models to constrain the physical conditions in the complex outflows. The temperature ...profile is consistent with a variable mass loss rate but the masers are mostly concentrated in dense clumps. High-excitation lines trace localised outflows near the star.
An extensive search has been conducted to confirm transitions of trans-ethyl methyl ether (tEME, C sub(2)H sub(5)OCH sub(3)), toward the high-mass star forming region W51 e1/e2 using the 12 m ...Telescope of the Arizona Radio Observatory at wavelengths from 2 mm and 3 mm. In short, we cannot confirm the detection of tEME toward W51 e1/e2 and our results call into question the initial identification of this species by Fuchs et al. Additionally, re-evaluation of the data from the original detection indicates that tEME is not present toward W51 e1/e2 in the abundance reported by Fuchs and colleagues. Typical peak-to-peak noise levels for the present observations of W51 e1/e2 were between 10 and 30 mK, yielding an upper limit of the tEME column density of < or =, slant1.5 x 10 super(15) cm super(-2). This would make tEME at least a factor of two times less abundant than dimethyl ether (CH sub(3)OCH sub(3)) toward W51 e1/e2. We also performed an extensive search for this species toward the high-mass star forming region Sgr B2(N-LMH) with the National Radio Astronomy Observatory 100 m Green Bank Telescope. No transitions of tEME were detected and we were able to set an upper limit to the tEME column density of < or =, slant4 x 10 super(14) cm super(-2) toward this source. Thus, we are able to show that tEME is not a new molecular component of the interstellar medium and that an exacting assessment must be carried out when assigning transitions of new molecular species to astronomical spectra to support the identification of large organic interstellar molecules.
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