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The pure rotational spectrum of the ScC2 radical ( X"2A1 ) has been measured using Fourier transform microwave/millimeter-wave techniques in the frequency range 15-63 GHz - the first high-resolution spectroscopic study of a 3d dicarbide species. ScC2 was created in a supersonic expansion from laser-ablated scandium and CH4 in the presence of a DC discharge. Four transitions, NKa,Kc = 101 → 000 through 404 → 303, were recorded, each consisting of multiple fine/hyperfine components; rotational, fine structure, and Sc(I = 7/2) hyperfine constants were determined. These measurements confirm the T-shaped geometry for ScC2, and suggest the molecule has significant covalent character. [ABSTRACT FROM AUTHOR]

Observations of HCN and HCO+ have been carried out toward 13 planetary nebulae (PNe) using the facilities of the Arizona Radio Observatory (ARO). These nebulae represent a wide range of morphologies and ages (∼2000â€"28,000 yr). For both molecules, the J = 1 â†' 0 transitions at 88â€"89 GHz and the J = 3 â†' 2 lines at 265â€"267 GHz were measured, together with CO lines (J = 1 â†' 0, 2 â†' 1, and 3 â†' 2, depending on the source), using the ARO 12 m and Submillimeter Telescopes. HCN and HCO+ were detected with at least one transition in 10 nebulae: He 2-459, Hu 1-1, K3-52, K3-65, M1-8, M1-40, M1-59, M2-53, M4-17, and NGC 6445. HCO+ was additionally identified via two transitions in Na 2. Some observed line profiles were complex, with multiple velocity components tracing varied outflows. From radiative transfer modeling, column densities were established for HCN and HCO+: N tot(HCN) = 0.005â€"1.1 Ă— 1014 and N tot(HCO+) = 0.008â€"9.5 Ă— 1013 cmâˆ'2. Gas densities of n (H2) ∼ 105â€"107 cmâˆ'3 were also determined for all PNe. Fractional abundances with respect to H2, calculated using CO as a proxy, are f (HCN) ∼ 0.2â€"1.5 Ă— 10âˆ'7 and f (HCO+) ∼ 0.3â€"5.1 Ă— 10âˆ'8. The abundances of HCN and HCO+ did not significantly vary with nebular age to 28,000 yr. Combined with previous observations, at least 30 PNe contain HCN and/or HCO+, indicating that polyatomic molecules are common constituents of these objects. The data strongly support a scenario where dense ejecta from PNe seed the interstellar medium with molecular material. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The pure rotational spectrum of KSH (X1A′) has been measured using millimeter-wave direct absorption and Fourier transform microwave (FTMW) techniques. This work is the first gas-phase experimental study of this molecule and includes spectroscopy of KSD as well. In the millimeter-wave system, KSH was synthesized in a DC discharge from a mixture of potassium vapor, H2S, and argon; a discharge-assisted laser ablation source, coupled with a supersonic jet expansion, was used to create the species in the FTMW instrument. Five and three rotational transitions in the range 3-57 GHz were recorded with the FTMW experiment for KSH and KSD, respectively, in the Ka = 0 component; in these data, potassium quadrupole hyperfine structure was observed. Five to six transitions with Ka = 0-5 were measured in the mm-wave region (260-300 GHz) for the two species. The presence of multiple asymmetry components in the mm-wave spectra indicates that KSH has a bent geometry, in analogy to other alkali hydrosulfides. The data were analyzed with an S-reduced asymmetric top Hamiltonian, and rotational, centrifugal distortion, and potassium electric quadrupole coupling constants were determined for both isotopolgues. The r0 geometry for KSH was calculated to be rS-H = 1.357(1) Å, rK-S = 2.806(1) Å, and θM-S-H (°) = 95.0 (1). FTMW measurements were also carried out on LiSH and NaSH; metal electric quadrupole coupling constants were determined for comparison with KSH. In addition, ab initio computations of the structures and vibrational frequencies at the CCSD(T)/6-311++G(3df,2pd) and CCSD(T)/aug-cc-pVTZ levels of theory were performed for LiSH, NaSH, and KSH. Overall, experimental and computational data suggest that the metal-ligand bonding in KSH is a combination of electrostatic and covalent forces. [ABSTRACT FROM AUTHOR]

The pure rotational spectrum of the ZnCCH (X2Σ+) 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, 64ZnCCH, and between 4 and 10 for the 66ZnCCH, 68ZnCCH, 64ZnCCD, and 64Zn13C13CH 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 2Σ Hamiltonian, and rotational, spin-rotation, and H, D, and 13C hyperfine parameters have been established for this radical. From the rotational constants, an rm(1) structure was determined with rZn-C = 1.9083 Å, rC-C = 1.2313 Å, and rC-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 2Π state may exist ∼19 000 cm-1 in energy above the ground state. [ABSTRACT FROM AUTHOR]

The pure rotational spectrum of the PCN radical (X3Σ-) has been measured for the first time using a combination of millimeter/submillimeter direct absorption and Fourier transform microwave (FTMW) spectroscopy. In the millimeter instrument, PCN was created by the reaction of phosphorus vapor and cyanogen in the presence of an ac discharge. A pulsed dc discharge of a dilute mixture of PCl3 vapor and cyanogen in argon was the synthetic method employed in the FTMW machine. Twenty-seven rotational transitions of PCN and six of P13CN in the ground vibrational state were recorded from 19 to 415 GHz, all which exhibited fine structure arising from the two unpaired electrons in this radical. Phosphorus and nitrogen hyperfine splittings were also resolved in the FTMW data. Rotational satellite lines from excited vibrational states with v2 = 1-3 and v1 = 1 were additionally measured in the submillimeter range. The data were analyzed with a Hund's case (b) effective Hamiltonian and rotational, fine structure, and hyperfine constants were determined. From the rotational parameters of both carbon isotopologues, the geometry of PCN was established to be linear, with a P-C single bond and a C-N triple bond, structurally comparable to other non-metal main group heteroatom cyanides. Analysis of the hyperfine constants suggests that the two unpaired electrons reside almost exclusively on the phosphorus atom in a π2 configuration, with little interaction with the nitrogen nucleus. The fine structure splittings in the vibrational satellite lines differ significantly from the pattern of the ground state, with the effect most noticeable with increasing v2 quantum number. These deviations likely result from spin-orbit vibronic perturbations from a nearby 1Σ+ state, suggested by the data to lie ∼12 000 cm-1 above the ground state. [ABSTRACT FROM AUTHOR]

The pure rotational spectrum of CuCCH in its ground electronic state (X 1Σ+) has been measured in the frequency range of 7-305 GHz using Fourier transform microwave (FTMW) and direct absorption millimeter/submillimeter methods. This work is the first spectroscopic study of CuCCH, a model system for copper acetylides. The molecule was synthesized using a new technique, discharge assisted laser ablation spectroscopy (DALAS). Four to five rotational transitions were measured for this species in six isotopologues (63CuCCH, 65CuCCH, 63Cu13CCH, 63CuC13CH, 63Cu13C13CH, and 63CuCCD); hyperfine interactions arising from the copper nucleus were resolved, as well as smaller splittings in CuCCD due to deuterium quadrupole coupling. Five rotational transitions were also recorded in the millimeter region for 63CuCCH and 65CuCCH, using a Broida oven source. The combined FTMW and millimeter spectra were analyzed with an effective Hamiltonian, and rotational, electric quadrupole (Cu and D) and copper nuclear spin-rotation constants were determined. From the rotational constants, an rm(2) structure for CuCCH was established, with rCu[Single_Bond]C=1.8177(6) Å, rC[Single_Bond]C=1.2174(6) Å, and rC[Single_Bond]H=1.046(2) Å. The geometry suggests that CuCCH is primarily a covalent species with the copper atom singly bonded to the C=C[Single_Bond]H moiety. The copper quadrupole constant indicates that the bonding orbital of this atom may be sp hybridized. The DALAS technique promises to be fruitful in the study of other small, metal-containing molecules of chemical interest. [ABSTRACT FROM AUTHOR]

The pure rotational spectrum of CCP (X 2Πr) has been measured at microwave, millimeter, and submillimeter wavelengths (17–545 GHz), along with its 13C isotopologues (13C13CP, C13CP, and 13CCP). The spectra of these species were recorded using a combination of millimeter/submillimeter direct absorption methods and Fourier transform microwave (FTMW) techniques. The phosphorus dicarbides were created in the gas phase from the reaction of red phosphorus and acetylene or methane in argon in an ac discharge for the direct absorption experiments, and using PCl3 as the phosphorus source in a pulsed dc nozzle discharge for the FTMW measurements. A total of 35 rotational transitions were recorded for the main isotopologue, and between 2 and 8 for the 13C-substituted species. Both spin-orbit components were identified for CCP, while only the Ω=1/2 ladder was observed for 13C13CP, C13CP, and 13CCP. Hyperfine splittings due to phosphorus were observed for each species, as well as carbon-13 hyperfine structure for each of the 13C-substituted isotopologues. The data were fitted with a Hund’s case (a) Hamiltonian, and rotational, fine structure, and hyperfine parameters were determined for each species. The rm(1) bond lengths established for CCP, r(C[Single_Bond]C)=1.289(1) Å and r(C[Single_Bond]P)=1.621(1) Å, imply that there are double bonds between both the two carbon atoms and the carbon and phosphorus atoms. The hyperfine constants suggest that the unpaired electron in this radical is primarily located on the phosphorus nucleus, but with some electron density also on the terminal carbon atom. There appears to be a minor resonance structure where the unpaired electron is on the nucleus of the end carbon. The multiple double bond structure forces the molecule to be linear, as opposed to other main group dicarbides, such as SiC2, which have cyclic geometries. [ABSTRACT FROM AUTHOR]

The pure rotational spectrum of cobalt monofluoride in its X 3[uppercase_phi_synonym]i electronic state has been measured in the frequency range of 256–651 GHz using direct absorption techniques. CoF was created by reacting cobalt vapor with F2 in helium at low pressure (25–30 mTorr). All three spin components were identified in the spectrum of this species, two of which exhibited lambda doubling. Each spin component showed hyperfine splittings from both nuclei: an octet pattern arising from the 59Co spin of I=7/2, which is further split into doublets due to the 19F nucleus (I=1/2). The data were fitted close to experimental precision using an effective Hamiltonian expressed in Hund’s case (a) form, and rotational, fine structure, hyperfine, and lambda-doubling parameters were determined. There is evidence that the rotational levels of the highest spin component 3[uppercase_phi_synonym]2 are perturbed. The r0 bond length of CoF was estimated from the rotational constant to be 1.738 014(1) Å. This value is in good agreement with previous studies but much more accurate. The matrix elements necessary for the complete treatment of Λ doubling in a [uppercase_phi_synonym] state have been derived and are presented for the first time. [ABSTRACT FROM AUTHOR]

The pure rotational spectrum of the SrSH radical in its ground electronic (&Xtilde; ²A′) and vibrational states has been measured using millimeter/submillimeter-wave direct absorption techniques. This work is the first observation of SrSH with rotational resolution. The spectrum of its deuterium isotopomer SrSD and SrS (X ¹∑[sup +)] has been recorded as well. These species were created by the reaction of strontium vapor and H[sub 2]S, in the presence of a dc discharge. SrS was also made with CS[sub 2]. For SrSH and SrSD, eight rotational transitions were recorded, respectively, for which asymmetry components up to K[sub a] = 8 were measured; fine structure was also resolved in each component. Thirteen transitions of SrS in each of its υ = 0, 1, and 2 states have additionally been observed. These data have been analyzed and spectroscopic parameters determined for all three species, including spin-rotation terms for the strontium hydrosulfides. From an r[sub 0] structure calculation, the bond angle in SrSH was determined to be 91.48(3)°, very close to that of H[sub 2]S and CaSH. This geometry indicates that SrSH is a covalently bonded molecule, as opposed to linear (and ionic) SrOH. The Sr-S bond length in SrSH was also found to be greater than that of SrS (r[sub Sr-S] = 2.705 Å versus 2.441 Å), indicating a change in bond order. In addition, the spin-rotation interaction in SrSH and SrSD includes a small contribution from the off-diagonal term, (ε[sub ab] + ε[sub ba])/2, resulting from the crossing of energy levels with ΔJ = 0, ΔK[sub a] = ± 1. Second-order spin-orbit coupling appears to make a significant contribution to the spin-rotation splitting, as well, which must arise from mixing of the à ²A&′ and &Btilde; ²A″ excited states. © 2001 American Institute of Physics. [DOI: 10.1063/1.1419060]. [ABSTRACT FROM AUTHOR]

The millimeter/submillimeter spectrum of magnesium chloride (MgCl) has been observed in two new electronic excited states, (3) 2 Σ + and (4) 2 Σ + , using direct absorption methods. The molecule was synthesized in a mixture of Cl 2 , argon, and magnesium vapor. For the (3) 2 Σ + state, multiple rotational transitions were measured in the v = 0 level for all six isotopologues ( 24 Mg 35 Cl, 24 Mg 37 Cl, 25 Mg 35 Cl, 25 Mg 37 Cl, 26 Mg 35 Cl, and 26 Mg 37 Cl), as well as up to v = 13 for 24 Mg 35 Cl. For the (4) 2 Σ + state, less intense spectra were recorded for 24 Mg 35 Cl ( v = 0-2). Equilibrium rotational parameters were determined for both states for 24 Mg 35 Cl, as well as rotational constants and 25 Mg hyperfine parameters for the other isotopologues. A perturbation was observed between rotational levels of the two states due to an avoided crossing. Computations were also carried out at the CASPT2 and MRCISD+Q levels, and the resulting bond lengths for (3) 2 Σ + and (4) 2 Σ + states agree well with the experimental values of r e = 2.536 and 2.361 Å. The computations show that the (3) 2 Σ + state has a double-well potential; however, the state behaves as a single well with unperturbed vibrational levels up to v = 13 due to nonadiabatic interactions with the (4) 2 Σ + state.

Despite its importance in planet formation and biology 1 , phosphorus has been identified only in the inner 12 kpc of the Galaxy 2-19 . The study of this element has been hindered in part by unfavourable atomic transitions 2,4,20 . Phosphorus is thought to be created by neutron capture on 29 Si and 30 Si in massive stars 20,21 , and released into the interstellar medium by Type II supernova explosions 2,22 . However, models of galactic chemical evolution must arbitrarily increase the supernovae production 23 to match observed abundances. Here we present the detection of gas-phase phosphorus in the Outer Galaxy through millimetre spectra of PO and PN. Rotational lines of these molecules were observed in the dense cloud WB89-621, located 22.6 kpc from the Galactic Centre 24 . The abundances of PO and PN in WB89-621 are comparable to values near the Solar System 25 . Supernovae are not present in the Outer Galaxy 26 , suggesting another source of phosphorus, such as 'Galactic Fountains', where supernova material is redistributed through the halo and circumgalactic medium 27 . However, fountain-enriched clouds are not found at such large distances. Any extragalactic source, such as the Magellanic Clouds, is unlikely to be metal rich 28 . Phosphorus instead may be produced by neutron-capture processes in lower mass asymptotic giant branch stars 29 which are present in the Outer Galaxy. Asymptotic giant branch stars also produce carbon 21 , flattening the extrapolated metallicity gradient and accounting for the high abundances of C-containing molecules in WB89-621., (© 2023. The Author(s).)

The millimeter/submillimeter-wave spectrum of the SiP radical (X 2 Π i ) has been recorded using direct absorption spectroscopy in the frequency range of 151-532 GHz. SiP was synthesized in an AC discharge from the reaction of SiH 4 and gas-phase phosphorus, in argon carrier gas. Both spin-orbit ladders were observed. Fifteen rotational transitions were measured originating in the Ω = 3/2 ladder, and twelve in the Ω = 1/2 substate, each exhibiting lambda doubling and, at lower frequencies, hyperfine interactions from the phosphorus nuclear spin of I = 1/2. The lambda-doublets in the Ω = 1/2 levels appeared to be perturbed at higher J, with the f component deviating from the predicted pattern, likely due to interactions with the nearby excited A 2 Σ + electronic state, where ΔE Π-Σ ∼ 430 cm -1 . The data were analyzed using a Hund's case a β Hamiltonian and rotational, spin-orbit, lambda-doubling, and hyperfine parameters were determined. A 2 Π/ 2 Σ deperturbation analysis was also performed, considering spin-orbit, spin-electronic, and L-uncoupling interactions. Although SiP is clearly not a hydride, the deperturbed parameters derived suggest that the pure precession hypothesis may be useful in assessing the 2 Π/ 2 Σ interaction. Interpretation of the Fermi contact term, b F , the spin-dipolar constant, c, and the nuclear spin-orbital parameter, a, indicates that the orbital of the unpaired electron is chiefly p π in character. The bond length in the v = 0 level was found to be r 0 = 2.076 Å, suggestive of a double bond between the silicon and phosphorus atoms.

The millimeter/submillimeter spectrum of the CrBr radical has been recorded in the frequency range of 220-300 GHz using direct absorption techniques, utilizing a new instrumental design. This study is the first spectroscopic investigation of this radical species by any method. CrBr was synthesized in a DC discharge by the reaction of chromium vapor, produced in a Broida-type oven, with Br 2 CH 2 in argon. Six to nine rotational transitions were measured for four isotopologues of this molecule in their natural abundances, 52 Cr 79 Br, 52 Cr 81 Br, 53 Cr 79 Br, and 53 Cr 81 Br. Each transition was found to consist of six distinct fine structure components, indicating a 6 Σ + ground electronic state, as observed for CrF and CrCl. Lines originating in the v = 1 and 2 vibrational states were recorded for 52 Cr 79 Br and 52 Cr 81 Br as well. The spectra were analyzed using a Hund's case (b) Hamiltonian, and rotational, spin-spin, and spin-rotation parameters were determined. The third-order spin-rotation constant γ s and the fourth order spin-spin term θ were necessary for the analysis; these parameters are thought to play a role in states with high multiplicities. Equilibrium parameters were also derived for the CrBr; a bond length of r e = 2.337 282 (30) Å and a vibrational constant of ω e ≅ 300 cm -1 were determined. The sign and magnitude of the spin-spin and spin-rotation constants suggest the presence of nearby 4 Π and 6 Π excited states in CrBr, lying ∼9000 cm -1 above the ground state. The new instrument design, employing more compact, free-space optics utilizing an offset ellipsoidal mirror, facilitated these measurements.

The pure rotational spectrum of ZnBr (X 2 Σ + ) has been recorded in the frequency range 259-310 GHz using millimeter-wave direct absorption techniques. This study is the first quantitative spectroscopic investigation of this free radical. ZnBr was synthesized in a DC discharge by the reaction of zinc vapor in argon with one of three reagents: BrCH 3 , Br 2 CH 2 , or Br 2 . Eight rotational transitions were measured for six isotopologues ( 64 Zn 79 Br, 64 Zn 81 Br, 66 Zn 79 Br, 66 Zn 81 Br, 68 Zn 79 Br, and 68 Zn 81 Br), all of which exhibited spin-rotation interactions. Furthermore, transitions originating in the v = 1 through 3 excited vibrational states were obtained for certain isotopologues. Five rotational transitions were also recorded for 67 Zn 79 Br, in which hyperfine splittings were observed arising from the 67 Zn nucleus (I = 5/2). The spectra were analyzed using a Hund's case (b βJ ) Hamiltonian, and rotational, spin-rotation, and 67 Zn magnetic hyperfine constants were determined. Equilibrium parameters were also derived for the 64 Zn 79 Br, 64 Zn 81 Br, 66 Zn 79 Br, and 66 Zn 81 Br isotopologues, including the vibrational constant, ω e = 286 cm -1 . The equilibrium bond length was derived to be r e = 2.268 48(90) Å. Analysis of the 67 Zn hyperfine parameters suggest a decrease in ionic character in ZnBr from the other known zinc halides, ZnF and ZnCl.

Carbon, nitrogen and oxygen are the three most abundant elements in the Galaxy after hydrogen and helium. Whereas hydrogen and helium were created in the Big Bang, carbon, nitrogen and oxygen arise from nucleosynthesis in stars. Of particular interest 1,2 are the isotopic ratios 12 C/ 13 C, 14 N/ 15 N and 16 O/ 17 O because they are effective tracers of nucleosynthesis and help to benchmark the chemical processes that occurred in primitive interstellar material as it evolved into our Solar System 3 . However, the origins of the rare isotopes 15 N and 17 O remain uncertain, although novae and very massive stars that explode as supernovae are postulated 4-6 to be the main sources of 15 N. Here we report millimetre-wavelength observations of the young bipolar planetary nebula K4-47 that indicate another possible source for these isotopes. We identify various carbon-bearing molecules in K4-47 that show that this object is carbon-rich, and find unusually high enrichment in rare carbon ( 13 C), oxygen ( 17 O) and nitrogen ( 15 N) isotopes: 12 C/ 13 C = 2.2 ± 0.8, 16 O/ 17 O = 21.4 ± 10.3 and 14 N/ 15 N = 13.6 ± 6.5 (uncertainties are three standard deviations); for comparison, the corresponding solar ratios 7 are 89.4 ± 0.2, 2,632 ± 7 and 435 ± 57. One possible interpretation of these results is that K4-47 arose from a J-type asymptotic giant branch star that underwent a helium-shell flash (an explosive nucleosynthetic event that converts large quantities of helium to carbon and other elements), enriching the resulting planetary nebula in 15 N and 17 O and creating its bipolar geometry. Other possible explanations are that K4-47 is a binary system or that it resulted from a white dwarf merger, as has been suggested for object CK Vul 8 . These results suggest that nucleosynthesis of carbon, nitrogen and oxygen is not well understood and that the classification of certain stardust grains must be reconsidered.

The pure rotational spectrum of the AlC2 radical (X[combining tilde]2A1) has been measured using Fourier transform microwave/millimeter-wave (FTMmmW) techniques in the frequency range 21-65 GHz. This study is the first high-resolution spectroscopic investigation of this molecule. AlC2 was created in a supersonic jet from the reaction of aluminum, generated by laser ablation, with a mixture of CH4 or HCCH, diluted in argon, in the presence of a DC discharge. Three transitions (NKa,Kc = 101 → 000, 202 → 101, and 303 → 202) were measured, each consisting of multiple fine/hyperfine components, resulting from the unpaired electron in the species and the aluminum-27 nuclear spin (I = 5/2). The data were analyzed using an asymmetric top Hamiltonian and rotational, fine structure, and hyperfine constants determined. These parameters agree well with those derived from previous theoretical calculations and optical spectra. An r0 structure of AlC2 was determined with r(Al-C) = 1.924 Å, r(C-C) = 1.260 Å, and θ(C-Al-C) = 38.2°. The Al-C bond was found to be significantly shorter than in other small, Al-bearing species. The Fermi contact term established in this work indicates that the unpaired electron in the valence orbital has considerable 3pza1 character, suggesting polarization towards the C2 moiety. A high degree of ionic character in the molecule is also evident from the quadrupole coupling constant. These results are consistent with a T-shaped geometry and an Al+C2- bonding scheme. AlC2 is a possible interstellar molecule that may be present in the circumstellar envelopes of carbon-rich AGB stars.

The pure rotational spectrum of the ZnSH (X̃ 2 A') radical has been measured using millimeter-wave direct absorption and Fourier transform microwave (FTMW) methods across the frequency range 18-468 GHz. This work is the first gas-phase detection of ZnSH by any spectroscopic technique. Spectra of the 66 ZnSH, 68 ZnSH, and 64 ZnSD isotopologues were also recorded. In the mm-wave study, ZnSH was synthesized in a DC discharge by the reaction of zinc vapor, generated by a Broida-type oven, with H 2 S; for FTMW measurements, the radical was made in a supersonic jet expansion by the same reactants but utilizing a discharge-assisted laser ablation source. Between 7 and 9 rotational transitions were recorded for each isotopologue. Asymmetry components with K a = 0 through 6 were typically measured in the mm-wave region, each split into spin-rotation doublets. In the FTMW spectra, hyperfine interactions were also resolved, arising from the hydrogen or deuterium nuclear spins of I = 1/2 or I = 1, respectively. The data were analyzed using an asymmetric top Hamiltonian, and rotational, spin-rotation, and magnetic hyperfine parameters were determined for ZnSH, as well as the quadrupole coupling constant for ZnSD. The observed spectra clearly indicate that ZnSH has a bent geometry. The r m (1) structure was determined to be r Zn-S = 2.213(5) Å, r S-H = 1.351(3) Å, and θ Zn-S-H = 90.6(1)°, suggesting that the bonding occurs primarily through sulfur p orbitals, analogous to H 2 S. The hyperfine constants indicate that the unpaired electron in ZnSH primarily resides on the zinc nucleus.

The chemical history of carbon is traced from its origin in stellar nucleosynthesis to its delivery to planet surfaces. The molecular carriers of this element are examined at each stage in the cycling of interstellar organic material and their eventual incorporation into solar system bodies. The connection between the various interstellar carbon reservoirs is also examined. Carbon has two stellar sources: supernova explosions and mass loss from evolved stars. In the latter case, the carbon is dredged up from the interior and then ejected into a circumstellar envelope, where a rich and unusual C-based chemistry occurs. This molecular material is eventually released into the general interstellar medium through planetary nebulae. It is first incorporated into diffuse clouds, where carbon is found in polyatomic molecules such as H 2 CO, HCN, HNC, c-C 3 H 2 , and even C 60 + . These objects then collapse into dense clouds, the sites of star and planet formation. Such clouds foster an active organic chemistry, producing compounds with a wide range of functional groups with both gas-phase and surface mechanisms. As stars and planets form, the chemical composition is altered by increasing stellar radiation, as well as possibly by reactions in the presolar nebula. Some molecular, carbon-rich material remains pristine, however, encapsulated in comets, meteorites, and interplanetary dust particles, and is delivered to planet surfaces. Key Words: Carbon isotopes-Prebiotic evolution-Interstellar molecules-Comets-Meteorites. Astrobiology 16, 997-1012.

Pure rotational spectroscopy of the CrC (X(3)Σ(-)) and CrCCH (X̃ (6)Σ(+)) radicals has been conducted using millimeter/sub-millimeter direct absorption methods in the frequency range 225-585 GHz. These species were created in an AC discharge of Cr(CO)6 and either methane or acetylene, diluted in argon. Spectra of the CrCCD were also recorded for the first time using deuterated acetylene as the carbon precursor. Seven rotational transitions of CrC were measured, each consisting of three widely spaced, fine structure components, arising from spin-spin and spin-rotation interactions. Eleven rotational transitions were recorded for CrCCH and five for CrCCD; each transition in these cases was composed of a distinct fine structure sextet. These measurements confirm the respective (3)Σ(-) and (6)Σ(+) ground electronic states of these radicals, as indicated from optical studies. The data were analyzed using a Hund's case (b) Hamiltonian, and rotational, spin-spin, and spin-rotation constants have been accurately determined for all three species. The spectroscopic parameters for CrC were significantly revised from previous optical work, while those for CrCCH are in excellent agreement; completely new constants were established for CrCCD. The chromium-carbon bond length for CrC was calculated to be 1.631 Å, while that in CrCCH was found to be rCr-C = 1.993 Å - significantly longer. This result suggests that a single Cr-C bond is present in CrCCH, preserving the acetylenic structure of the ligand, while a triple bond exists in CrC. Analysis of the spin constants suggests that CrC has a nearby excited (1)Σ(+) state lying ∼16 900 cm(-1) higher in energy, and CrCCH has a (6)Π excited state with E ∼ 4800 cm(-1).

An ever increasing amount of molecular material is being discovered in the interstellar medium, associated with the birth and death of stars and planetary systems. Radio and millimeter-wave astronomical observations, made possible by high-resolution laboratory spectroscopy, uniquely trace the history of gas-phase molecules with biogenic elements. Using a combination of both disciplines, the full extent of the cycling of molecular matter, from circumstellar ejecta of dying stars - objects which expel large amounts of carbon - to nascent solar systems, has been investigated. Such stellar ejecta have been found to exhibit a rich and varied chemical content. Observations demonstrate that this molecular material is passed onto planetary nebulae, the final phase of stellar evolution. Here the star sheds almost its entire original mass, becoming an ultraviolet-emitting white dwarf. Molecules such as H2CO, HCN, HCO(+), and CCH are present in significant concentrations across the entire age span of such nebulae. These data suggest that gas-phase polyatomic, carbon-containing molecules survive the planetary nebula phase and subsequently are transported into the interstellar medium, seeding the chemistry of diffuse and then dense clouds. The extent of the chemical complexity in dense clouds is unknown, hindered by the high spectral line density. Organic species such as acetamide and methyl amine are present in such objects, and NH2CHO has a wide Galactic distribution. However, organophosphorus compounds have not yet been detected in dense clouds. Based on carbon and nitrogen isotope ratios, molecular material from the ISM appears to become incorporated into solar system planetesimals. It is therefore likely that interstellar synthesis influences prebiotic chemistry on planet surfaces.

The pure rotational spectrum of KSH (X(1)A') has been measured using millimeter-wave direct absorption and Fourier transform microwave (FTMW) techniques. This work is the first gas-phase experimental study of this molecule and includes spectroscopy of KSD as well. In the millimeter-wave system, KSH was synthesized in a DC discharge from a mixture of potassium vapor, H2S, and argon; a discharge-assisted laser ablation source, coupled with a supersonic jet expansion, was used to create the species in the FTMW instrument. Five and three rotational transitions in the range 3-57 GHz were recorded with the FTMW experiment for KSH and KSD, respectively, in the K(a) = 0 component; in these data, potassium quadrupole hyperfine structure was observed. Five to six transitions with K(a) = 0-5 were measured in the mm-wave region (260-300 GHz) for the two species. The presence of multiple asymmetry components in the mm-wave spectra indicates that KSH has a bent geometry, in analogy to other alkali hydrosulfides. The data were analyzed with an S-reduced asymmetric top Hamiltonian, and rotational, centrifugal distortion, and potassium electric quadrupole coupling constants were determined for both isotopolgues. The r0 geometry for KSH was calculated to be r(S-H) = 1.357(1) Å, r(K-S) = 2.806(1) Å, and θ(M-S-H) (°) = 95.0 (1). FTMW measurements were also carried out on LiSH and NaSH; metal electric quadrupole coupling constants were determined for comparison with KSH. In addition, ab initio computations of the structures and vibrational frequencies at the CCSD(T)/6-311++G(3df,2pd) and CCSD(T)/aug-cc-pVTZ levels of theory were performed for LiSH, NaSH, and KSH. Overall, experimental and computational data suggest that the metal-ligand bonding in KSH is a combination of electrostatic and covalent forces.

The pure rotational spectrum of FeCN has been recorded in the frequency range 140-500 GHz using millimeter/sub-millimeter direct absorption techniques. The species was created in an ac discharge of Fe(CO)(5) and cyanogen. Spectra of the (13)C, (54)Fe, and (57)Fe isotopologues were also measured, confirming the linear cyanide structure of this free radical. Lines originating from several Renner-Teller components in the ν(2) bending mode were also observed. Based on the observed spin-orbit pattern, the ground state of FeCN is (4)Δ(i), with small lambda-doubling splittings apparent in the Ω = 5/2, 3/2, and 1/2 components. In addition, a much weaker spectrum of the lowest spin-orbit component of FeNC, Ω = 9/2, was recorded; these data are consistent with the rotational parameters of previous optical studies. The data for FeCN were fit with a Hund's case (a) Hamiltonian and rotational, spin-orbit, spin-spin, and lambda-doubling parameters were determined. Rotational constants were also established from a case (c) analysis for the other isotopologues, excited vibronic states, and for FeNC. The r(0) bond lengths of FeCN were determined to be r(Fe-C) = 1.924 Å and r(C-N) = 1.157 Å, in agreement with theoretical predictions for the (4)Δ(i) state. These measurements indicate that FeCN is the lower energy isomer and is more stable than FeNC by ~1.9 kcal/mol., (© 2011 American Institute of Physics)

The pure rotational spectrum of the CrS radical has been measured in its ground X (5)Π(r) state using gas-phase millimeter/submillimeter direct absorption methods. The molecule was created by the reaction of chromium vapor, sublimed in a Broida-type oven, with hydrogen sulfide. Eleven rotational transitions were recorded for this free radical in the frequency range of 280-405 GHz; in most transitions, all five spin components were observed, and lambda-doubling was resolved in the Ω=0, 1, and 2 ladders. The data were fit with a Hund's case (a) Hamiltonian and rotational, spin-orbit, spin-spin, and lambda-doubling constants were established. Higher order spin and spin-orbit terms were essential in the analysis. The lambda-doubling constants indicate a nearby (5)Σ(+) state at an energy of ∼1500-2000 cm(-1). A bond length of 2.0781 Å was derived for CrS from the data, which is larger than the value of 2.0682 Å found for MnS by ∼0.01 Å. In contrast, the bond distance for MnO is greater than that of CrO by 0.03 Å, an illustration of the subtle differences between 3d oxide and sulfides. CrS is the second molecule in a (5)Π state that has been studied by rotational spectroscopy.

The pure rotational spectrum of CuCCH in its ground electronic state (X̃  (1)Σ(+)) has been measured in the frequency range of 7-305 GHz using Fourier transform microwave (FTMW) and direct absorption millimeter/submillimeter methods. This work is the first spectroscopic study of CuCCH, a model system for copper acetylides. The molecule was synthesized using a new technique, discharge assisted laser ablation spectroscopy (DALAS). Four to five rotational transitions were measured for this species in six isotopologues ((63)CuCCH, (65)CuCCH, (63)Cu(13)CCH, (63)CuC(13)CH, (63)Cu(13)C(13)CH, and (63)CuCCD); hyperfine interactions arising from the copper nucleus were resolved, as well as smaller splittings in CuCCD due to deuterium quadrupole coupling. Five rotational transitions were also recorded in the millimeter region for (63)CuCCH and (65)CuCCH, using a Broida oven source. The combined FTMW and millimeter spectra were analyzed with an effective Hamiltonian, and rotational, electric quadrupole (Cu and D) and copper nuclear spin-rotation constants were determined. From the rotational constants, an r(m)(2) structure for CuCCH was established, with r(Cu-C) = 1.8177(6) Å, r(C-C) = 1.2174(6) Å, and r(C-H) = 1.046(2) Å. The geometry suggests that CuCCH is primarily a covalent species with the copper atom singly bonded to the C≡C-H moiety. The copper quadrupole constant indicates that the bonding orbital of this atom may be sp hybridized. The DALAS technique promises to be fruitful in the study of other small, metal-containing molecules of chemical interest.

The pure rotational spectrum of the CCAs radical in its ground electronic and spin state, X (2)Pi(12), has been measured using Fourier transform microwave techniques in the frequency range of 12-40 GHz. This species was created in a supersonic expansion from a reaction mixture of AsCl(3) and C(2)H(2) or CH(4) diluted in high pressure argon, using a pulsed nozzle containing a dc discharge source. Three rotational transitions were measured for the main isotopologue, (12)C(12)CAs, in the Omega=12 ladder; both lambda-doubling and arsenic (I=32) hyperfine interactions were observed in these spectra. In addition, two to four rotational transitions were recorded for the (13)C(13)CAs, (13)C(12)CAs, and (12)C(13)CAs species. In these three isotopologues, hyperfine splittings were also resolved arising from the (13)C nuclei (I=12), creating complex spectral patterns. The CCAs spectra were analyzed with a case (a) Hamiltonian, and effective rotational, lambda-doubling, and arsenic and carbon-13 hyperfine constants were determined for the Omega=12 ladder. From the effective rotational constants of the four isotopologues, an r(m) ((1)) structure has been derived with r(C-C)=1.287 A and r(C-As)=1.745 A. These bond lengths indicate that the predominant structure for arsenic dicarbide is C=C=As, with some contributing C[Triple Bond]C and C[Triple Bond]As triple bond characters. The hyperfine constants established in this work indicate that about 23 of the unpaired electron density lies on the arsenic atom, with the remaining percentage on the terminal carbon. The value of the arsenic quadrupole coupling constant (eqQ=-202 MHz) suggests that the As-C bond has a mixture of covalent and ionic characters, consistent with theoretical predictions that both pi backbonding and electron transfer play a role in creating a linear, as opposed to a cyclic, structure for certain heteroatom dicarbides.

The pure rotational spectrum of the VCl radical in its (5)Delta(r) ground state has been recorded in the range 236-417 GHz using millimeter/submillimeter direct absorption techniques. This species was created in an ac discharge of VCl(4) and argon. Ten rotational transitions of V(35)Cl were measured in all five Omega ladders; an additional nine transitions of the Omega=1 spin state were recorded in order to evaluate the (51)V hyperfine structure. Hyperfine interactions associated with the (35)Cl nucleus were not resolved, consistent with the ionic structure of the molecule. Because of extensive perturbations caused by the low-lying A (5)Pi(r) excited state, the rotational spectrum of the ground state has been found to be quite irregular. The four lowest Omega ladders exhibit unusually large lambda-doubling interactions, with the Omega=1 component showing the largest splitting, over 2 GHz in magnitude. The Omega=1 transitions are also shifted to higher frequency relative to the other spin components. In addition, the hyperfine structure varies widely between the Omega ladders, and an avoided crossing is observed in two transitions of both the Omega=1e and 2e components. The data have been analyzed with a case (c) Hamiltonian, and effective rotational, lambda-doubling, and hyperfine constants have been determined for V(35)Cl. Higher-order parity-dependent magnetic hyperfine terms d(Delta2) and d(Delta3) were required in the analysis, derived from perturbation theory, in addition to the usual d(Delta) parameter. The local perturbations evident in these spectra indicate that the A (5)Pi(r) excited state lies within the spin-orbit manifold of the ground state, well below the predicted value of 517 cm(-1). Mixing of the A (5)Pi(r) and X (5)Delta(r) states apparently causes both local and global perturbations in the ground state spectrum.

The pure rotational spectrum of HZnCN in its X (1)Sigma(+) electronic state has been recorded using pulsed Fourier transform microwave (FTMW) techniques in the frequency range 7-39 GHz-the first spectroscopic study of this species in the gas phase. The FTMW spectrum of ZnCN(X (2)Sigma(+)) has been measured as well. A new FTMW spectrometer with an angled beam and simplified electronics, based on a cryopump, was employed for these experiments. The molecules were created in a dc discharge from a gas mixture of Zn(CH(3))(2) and cyanogen (1% D(2) for the deuterated analogs), diluted with argon, that was expanded supersonically from a pulsed nozzle. Seven isotopologues of HZnCN arising from zinc, deuterium, and (13)C substitutions were studied; for every species, between three and five rotational transitions were recorded, each consisting of numerous hyperfine components arising from nitrogen, and in certain cases, deuterium, and 67-zinc nuclear spins. Four transitions of ZnCN were measured. From these data, rotational, nuclear spin-rotation, and quadrupole coupling constants have been determined for HZnCN, as well as rotational, and magnetic and quadrupole hyperfine parameters for the ZnCN radical. The bond lengths determined for HZnCN are r(H-Zn)=1.495 A, r(Zn-C)=1.897 A, and r(C-N)=1.146 A, while those for ZnCN are r(Zn-C)=1.950 A and r(C-N)=1.142 A. The zinc-carbon bond length thus shortens with the addition of the H atom. The nitrogen quadrupole coupling constant eqQ was found to be virtually identical in both cyanide species (-5.089 and -4.931 MHz), suggesting that the electric field gradient across the N nucleus is not influenced by the H atom. The quadrupole constant for the (67)Zn nucleus in H(67)ZnCN is unusually large relative to that in (67)ZnF (-104.578 versus -60 MHz), evidence that the bonding in the cyanide has more covalent character than in the fluoride. This study additionally suggests that hydrides of other metal cyanide species are likely candidates for high resolution spectroscopic investigations.

The pure rotational spectrum of CCP (X (2)Pi(r)) has been measured at microwave, millimeter, and submillimeter wavelengths (17-545 GHz), along with its (13)C isotopologues ((13)C(13)CP, C(13)CP, and (13)CCP). The spectra of these species were recorded using a combination of millimeter/submillimeter direct absorption methods and Fourier transform microwave (FTMW) techniques. The phosphorus dicarbides were created in the gas phase from the reaction of red phosphorus and acetylene or methane in argon in an ac discharge for the direct absorption experiments, and using PCl(3) as the phosphorus source in a pulsed dc nozzle discharge for the FTMW measurements. A total of 35 rotational transitions were recorded for the main isotopologue, and between 2 and 8 for the (13)C-substituted species. Both spin-orbit components were identified for CCP, while only the Omega = 12 ladder was observed for (13)C(13)CP, C(13)CP, and (13)CCP. Hyperfine splittings due to phosphorus were observed for each species, as well as carbon-13 hyperfine structure for each of the (13)C-substituted isotopologues. The data were fitted with a Hund's case (a) Hamiltonian, and rotational, fine structure, and hyperfine parameters were determined for each species. The r(m)(1) bond lengths established for CCP, r(C-C) = 1.289(1) A and r(C-P) = 1.621(1) A, imply that there are double bonds between both the two carbon atoms and the carbon and phosphorus atoms. The hyperfine constants suggest that the unpaired electron in this radical is primarily located on the phosphorus nucleus, but with some electron density also on the terminal carbon atom. There appears to be a minor resonance structure where the unpaired electron is on the nucleus of the end carbon. The multiple double bond structure forces the molecule to be linear, as opposed to other main group dicarbides, such as SiC(2), which have cyclic geometries.

The pure rotational spectrum of cobalt monofluoride in its X (3)Phi(i) electronic state has been measured in the frequency range of 256-651 GHz using direct absorption techniques. CoF was created by reacting cobalt vapor with F(2) in helium at low pressure (25-30 mTorr). All three spin components were identified in the spectrum of this species, two of which exhibited lambda doubling. Each spin component showed hyperfine splittings from both nuclei: an octet pattern arising from the (59)Co spin of I=72, which is further split into doublets due to the (19)F nucleus (I=12). The data were fitted close to experimental precision using an effective Hamiltonian expressed in Hund's case (a) form, and rotational, fine structure, hyperfine, and lambda-doubling parameters were determined. There is evidence that the rotational levels of the highest spin component (3)Phi(2) are perturbed. The r(0) bond length of CoF was estimated from the rotational constant to be 1.738 014(1) A. This value is in good agreement with previous studies but much more accurate. The matrix elements necessary for the complete treatment of Lambda doubling in a Phi state have been derived and are presented for the first time.

Prebiotic possibilities for the synthesis of interstellar ribose through a protic variant of the formose reaction under gas-phase conditions were studied in the absence of any known catalyst. The ion-molecule reaction products, diose and triose, were sought by mass spectrometry, and relevant masses were observed. Ab initio calculations were used to evaluate protic formose mechanism possibilities. A bilateral theoretical and experimental effort yielded a physical model for glycoaldehyde generation whereby a hydronium cation can mediate formaldehyde dimerization followed by covalent bond formation leading to diose and water. These results advance the possibility that ion-molecule reactions between formaldehyde (CH(2)O) and H(3)O(+) lead to formose reaction products and inform us about potential sugar formation processes in interstellar space.

The millimeter/submillimeter-wave spectrum of the CoCl radical (X (3)Phi(i)) has been recorded using direct absorption techniques in the frequency range 340-510 GHz. This work is the first pure rotational study of this molecule. The radical was created by the reaction of Cl(2) with cobalt vapor. Rotational transitions arising from the Omega=4, 3, and 2 spin-orbit components of Co(35)Cl have been measured, all of which exhibit hyperfine splittings due to the (59)Co nucleus (I=7/2). Transitions arising from the Co(37)Cl species were also recorded, as well as those originating in the v=1, 2, 3, and 4 vibrational states of both isotopomers. The spin-orbit pattern exhibited by the molecule is unusual, with the Omega=3 component significantly shifted relative to the other spin components. In addition, the regular octet hyperfine splittings become distorted above a certain J value for the Omega=3 transitions only. These effects suggest that the molecule is highly perturbed in its ground state, most likely a result of second-order spin-orbit mixing with a nearby isoconfigurational (1)Phi(3) state. The complete data set for Co(35)Cl and Co(37)Cl were fit successfully with a case (a) Hamiltonian but required a large negative spin-spin constant of lambda=-7196 GHz and higher order centrifugal distortion corrections to the rotational, spin-orbit, spin-spin, and hyperfine terms. The value of the spin-spin constant suggests that the Omega=3 component is shifted to higher energy and lies near the Omega=2 sublevel. The hyperfine parameters are consistent with a delta(3)pi(3) electron configuration and indicate that CoCl is more covalent than CoF., ((c) 2004 American Institute of Physics.)

The pure rotational spectrum of the CoCN radical has been recorded in the frequency range 350-500 GHz using direct absorption techniques. This study is the first spectroscopic observation of this molecule by any experimental technique. Spectra of Co (13)CN have been measured as well. These data indicate that this species is linear in its ground electronic state and has the cyanide, as opposed to the isocyanide, geometry. The ground state term has been assigned as (3)Phi(i), based on the measurement of three spin components (Omega=4, 3, and 2) and in analogy to other isovalent cobalt-bearing species. Hyperfine splittings resulting from the (59)Co nuclear spin of I=7/2 were observed in every transition, each of which exhibited an octet pattern. For the lowest energy spin component, Omega=4, vibrational satellite features were also identified arising from the first quantum of the Co-C (v(1)=1) stretch and the v(2)=1 and v(2)=2 quanta of the bending mode, which were split by Renner-Teller interactions. The ground state measurements of CoCN were analyzed with a case a(beta) Hamiltonian, establishing rotational, fine structure, and hyperfine parameters. The vibrational and Co (13)CN spectra for the Omega=4 component were fit as well. An r(0) structure was also calculated, providing estimates of the Co-C and C-N bond distances, based on the Omega=4 transitions. CoCN is the fourth molecule in the 3d transition metal series to exhibit the linear cyanide structure, along with the Zn, Cu, and Ni analogs. The preference for this geometry, as opposed to the isocyanide form, may indicate a greater degree of covalent bonding in these species., ((c) 2004 American Institute of Physics.)

Interstellar hydrogen sulfide (H2S) and its isotopic variant (H2(34)S) have been observed toward several positions in OMC-1 via their 1(10)-1(01) transitions near 168 GHz using the FCRAO 14 m telescope. We derive total column densities toward Orion(KL) for the extended ridge, for the plateau, and for the hot core, in addition to values for other positions in OMC-1. The fractional abundance of H2S (approximately 10(-9)) in the quiescent regions of OMC-1 seems to be difficult to explain by currently known ion-molecule reactions. The fractional abundance of H2S relative to H2 is enhanced by a factor of 1000 in the hot core and the plateau relative to the quiescent clouds. This enhancement may be a result of grain surface chemistry and/or of high-temperature gas-phase chemistry. From the nondetection of HDS in its 2(11)-2(12) transition, we estimate the abundance ratio [HDS]/H2S] < or = 0.02 in the hot core.