Laboratory and Observational Studies of Transient Molecules at Microwave and Millimeter/Submillimeter Wavelengths

Abstract

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.