Pure rotational spectra of simple metal carbon clusters that relevant to transition metal synthesis and catalysis have been obtained using Fourier transform microwave (FTMW) techniques combined with millimeter-wave direct-absorption methods. Rotational spectra of metal acetylides (CuCCH, ZnCCH, Li/Na/KCCH, MgCCH, AlCCH, CrCCH), diatomic metal monocarbide (CrC) and T-shape metal dicarbides (YC₂ and ScC₂) were recorded in the 4–650 GHz frequency regime. Measurements of weaker isotoplogues including ⁶⁶ZnCCH, ⁶⁸ZnCCH, Zn¹³C¹³CH, ZnCCD, Li/Na/KCCD, CrCCD, Y¹³C¹²C, Y¹³C¹³C, Sc¹³C¹³C, were also studied to aid in structural determinations. This work is the first study of ZnCCH and ScC₂ by any type of spectroscopic technique. Hyperfine splittings in MgCCH and Li/Na/KCCH have also been resolved and the weak isotoplogues of YC₂ have been measured for the first time. Potential interstellar molecules ScO and FeCN were studied using the FTMW techniques in the 4–62 GHz frequency regime. Spectra of the zinc insertion product ClZnCH₃ were additionally recorded in the 10–30 GHz (FTMW) and 260–296 GHz (direct absorption) frequency ranges, along with weaker isotopologues Cl⁶⁶ZnCH₃ and Cl⁶⁸ZnCH₃. This works is the first measurement of zinc insertion products using the FTMW-DALAS techniques. The data were analyzed implementing an effective Hamiltonian, allowing for accurate spectroscopic parameters to be established. From rotational constants, the molecular geometries were accurately determined. Electronic properties were also assessed, including the degree of covalent vs ionic character in a chemical bond, and the molecular orbital composition. The fundamental physical and chemical properties of these benchmark species were obtained in order to gain insight into their role in larger molecular systems, test theoretical calculations, and, in certain cases, provide accurate rest frequencies for astronomical searches.

This dissertation describes the theoretical, laboratory, and astronomical spectroscopy of negative molecular ions (anions), starting with the laboratory detection of the large carbon chain anion C₆H⁻ in the radio band and its identification in the molecular envelope of the carbon star IRC+10216 and in the cold dark molecular cloud TMC-1. In IRC+10216 the identification solved the long standing problem of the unidentified series of lines with rotational constant 1377 MHz first observed by K. Kawaguchi et al. Rotational spectra of the structurally similar anions---CCH⁻, C₄H⁻, C₈H⁻, CN⁻, and C₃N⁻---have been detected in the laboratory, and three more anions---C₄H⁻, C₈H⁻, and C₃N⁻---have now been identified in space. Molecular structure calculations using the CCSD(T) method and large basis sets predicted accurately the rotational constants (B₀) and centrifugal distortion constants (D[subscript J]) of all six anions and their isotopomers, guiding laboratory searches for these species. Reported here are the radio spectra of C₄H⁻, C₆H⁻, C₈H⁻, and C₃N⁻, measured to within 0.1 ppm in the centimeter-wave band by Fourier transform microwave spectroscopy of supersonic molecular beams and in the millimeter-wave band by absorption spectroscopy of low-pressure DC discharges. The spectroscopic constants derived from these measurements are so accurate, that the rotational frequencies of the anions can be calculated to within 1 km s⁻¹, adequate for radio searches in essentially all astronomical molecular sources. Radio astronomical observations with the 100 m Green Bank Telescope (GBT) toward TMC-1 yielded detection of C₈H⁻, as well as an improved estimate of the column density of C₆H⁻. The two anions are surprisingly abundant relative to their neutral radicals: a C₆H⁻/C₆H ratio of 1.6% and a C₈H⁻/C₈H ratio of 5% was derived. Upper limits were obtained for C₄H⁻/C₄H (< 0.004%) and C₃N⁻/C₃N (< 0.8%). A survey of C₆H⁻ and the related radicals C₄H and C₆H was done with the GBT toward 24 galactic molecular sources. The C₆H⁻ ion was newly detected in two dark clouds: L1544 and L1521F; C₄H was detected in nearly all dark clouds surveyed (in six for the first time); and C₆H was newly detected in five dark clouds and a translucent cloud. The observed C₆H⁻/C₆H (1%-4%) and C₆H/C₄H (0.2%-1%) ratios suggest that C₆H⁻ may be close to detection in many other dark clouds. / text

No description available.

It was once thought that molecules in the interstellar medium (ISM) would be destroyed in the harsh surroundings and conditions of space, and therefore unobservable by radio techniques. However, it is now understood that the chemistry of the ISM is vast and complex. The question still remains as to just how complex is this chemistry. Much is clearly still not understood. This dissertation presents work on the study of metal compounds and cations in the circumstellar envelopes of oxygen- and carbon-rich asymptotic giant branch (AGB) and supergiant stars. Laboratory studies were also conducted on several transition metal compounds of interstellar interest, some with high spin and orbital angular momentum states. Work has been completed to confirm the detection of the debated metal cyanide KCN in the carbon-rich AGB star IRC+10216. KCN joins the list as the fifth interstellar metal cyanide/isocyanide detected in this source. In addition, preliminary results on the search for TiO are presented towards the oxygen-rich supergiant star, VY CMa. To further understand the evolutionary processes of carbon- and oxygen-rich stars, a survey of HCO⁺ was taken towards the carbon star IRC+10216, the oxygen-rich AGBs TX Cam, IK Tau, and W Hya and the oxygen-rich supergiant NML Cyg. While HCO⁺ was detected towards all of these sources, the results vary. The outflow of NML Cyg proves to be asymmetric and further study is necessary. The emission from W Hya is significantly narrower than the other sources. The abundances of HCO⁺ in circumstellar gas increases inversely with mass-loss rate and ion-molecule chemistry appears to influence the chemistry of evolved circumstellar envelopes. To understand species in space with more confidence, a laboratory search for several 3d transition metal species of astrochemical interest was conducted in the laboratory: HZnCl (X¹∑⁺), ZnO (X¹∑⁺ and a³Πᵢ), ZnCl (X²∑⁺), TiS (X³Δᵣ) and CrS (X⁵Πᵣ). All of the molecules have been observed for the first time with high resolution gas phase rotational spectroscopy and the work on ZnO was the first gas-phase study of this molecule. Synthesis of the species required exotic production methods, including use of a DC discharge to produce all zinc species. By studying the rotational spectra, rest frequencies were determined that will be beneficial for future astronomical searches.

Progress in our understanding of the chemical composition of the interstellar medium leans both on laboratory analyses of high resolution rotational spectra from molecules that may be present in these regions, and on radio astronomical observations of molecular tracers to constrain astrochemical models. Due to the thermodynamic conditions in outer space, some molecules likely to be found in interstellar regions in relevant abundances are open shell radicals. In a series of laboratory studies, the pure rotational spectra of the transition metal containing radicals sulfur species ScS, YS, VS and ZnSH were obtained for the first time. In addition to accurate and precise rest frequencies for these species, bonding characteristics were determined from fine and hyperfine molecular parameters. It was found that these sulfides have a higher degree of covalent bonding than their mostly ionic oxide counterparts. Isomers and isotope ratios are excellent diagnostic tools for a variety of astrochemical models. From radio observations of isotopes of nitrile species, the galactic gradient of ¹⁴N/¹⁵N was accurately established. A further study of this ratio in carbon rich asymptotic giant branch stars provided observational evidence for an unknown process in J type carbon stars, and highlighted the need to update stellar nucleosynthesis models. Proper radiative transfer modeling of the emission spectra of interstellar molecules can yield a wealth of information about the abundance and distribution of these species within the observed sources. To model the asymmetric emission of SO and SO₂ in oxygen-rich supergiants, an in-house code was developed, and successfully applied to gain insight into circumstellar sulfur chemistry of VY Canis Majoris. It was concluded that current astrochemistry kinetic models, based on spherical symmetry assumptions, need to be revisited.

Millimeter wave studies of molecules in circumstellar envelopes and a planetary nebula have been conducted. Using the Submillimeter Telescope (SMT) of the Arizona Radio Observatory (ARO) on Mt. Graham, a comparative spectral survey from 215-285 GHz was carried out of the carbon-rich asymptotic giant branch star IRC +10216 and the oxygen-rich supergiant VY Canis Majoris. A total of 858 emission lines were observed in both objects, arising from 40 different molecules. In VY Canis Majoris, AlO, AlOH, and PO were detected for the first time in interstellar space. In IRC +10216, PH3 was detected for the first time beyond the solar system, and C3O, and CH2NH were found for the first time in a circumstellar envelope. Additionally, in the evolved planetary nebula, the Helix, H2CO, C2H, and cyclic-C3H2 were observed using the SMT and the Kitt Peak 12 m telescopes. The presence of these three molecules in the Helix suggests that relatively complex chemistry occurs in planetary nebulae, despite the harsh ultraviolet field. Overall, the research on molecules in circumstellar and planetary nebulae furthers our understanding of the nature of the material that is fed back into the interstellar medium from evolved stars. Besides telescope work, laboratory research was also conducted - the rotational spectrum of ZnCl was measured and its bond length and rotational constants were determined. Lastly, in partial fulfillment of a graduate certificate in entrepreneurial chemistry, the commercial applications of terahertz spectroscopy were explored through literature research.

No description available.

In this dissertation, techniques of high-resolution rotational spectroscopy have been used to measure the spectra of molecules in both laboratory and astronomical settings. In the laboratory, small metal-bearing molecules containing zinc, iron, nickel, titanium, yttrium, and scandium have been studied at microwave and millimeter/submillimeter wavelengths in order to determine their rotational, fine, and hyperfine constants. These molecules were synthesized in situ in direct-absorption and Fourier-transform microwave spectrometers using Broida-type ovens and laser ablation methods. From the spectroscopic parameters, information about fundamental physical propertes and electronic character could be obtained. Radio telescopes were used to measure the spectra of molecules in different interstellar environments. A new molecule, FeCN, was detected toward the circumstellar envelope of the carbon-rich asymtotic giant branch star, IRC+10216, marking the first iron-bearing molecule detected in the interstellar medium. The telescopes were also used to conduct a study of the evolved planetary nebula, NGC 7293, or the Helix Nebula. In the Helix, CO, HCO⁺, and H₂CO were observed at several positions offset from the central star to obtain densities and kinetic temperatures throughout the Helix. A map of the HCO⁺ J = 1→ 0 transition was also constructed, showing that HCO⁺ is widespread throughout the Helix, instead of being photodissociated and destroyed, as theoretical models of planetary nebulae predict.

The rotational spectrum of ScO (X-2 Sigma(+)) has been measured in the gas phase in the frequency range 30-493 GHz using a combination of Fourier transform microwave/millimeter-wave (FTM/mmW) and submillimeter direct absorption methods. This work is the first pure rotational study of this radical. Both the ground vibrational and v=1 states were observed. ScO was created from the reaction of metal vapor, produced either by a laser ablation source or a Broida-type oven, and N2O, in the former case heavily diluted in argon. Extensive hyperfine structure was observed in the FTM/mmW data, although the spin-rotation splitting was found to be small (similar to 3 MHz). In the mm-wave spectra, however, the fine and hyperfine structure was blended together, resulting in broad, single lines for a given transition N + 1 <- N. The data were analyzed in a combined fit using the very accurate hyperfine measurements of Childs and Steimle (1988), employing a Hund's case b Hamiltonian, and an improved set of rotational and centrifugal distortion constants were determined. These measurements improve the accuracy of predicted frequencies for astronomical searches by 14-18 MHz, or 16-20 km/s, in the 1 mm region - a difference of half to a full linewidth for certain interstellar sources. This work also demonstrates the capabilities of the FTM/mmW spectrometer at 61 GHz.

No description available.