Rovibronic And Pure Rotational Spectra Of Transient Molecules

Transient species are of great importance to atmospheric chemistry, astrophysics, combustion, plasma and many other relevant fields. This dissertation is concerned with the spectroscopic study of the millimeter-wave, near infrared and visible absorption spectrum of gas phase transient species. The rovibronic spectrum of CN radical, N₂⁺ ion and CS⁺ ion generated in AC glow discharges and the pure rotational spectrum of HCBr radical produced by UV laser photolysis have been investigated.The (A²Î _i)-(X²Î£⁺) (2, 0) band of CN was reinvestigated in the AC glow discharge of CH₃CN with He as the carrier gas using near-infrared concentration modulation laser spectroscopy. All the twelve rotational branches of the (2, 0) band including four new branches were recorded in higher resolution than the previously measured emission spectrum and 189 lines were assigned. More precise TÏ…, AÏ…,BÏ…constants for the A²Î _i(Ï…'=2) state of CN were derived.The A²Î _u-X²Î£g⁺ transition of N₂⁺ has been extensively studied by various spectroscopic techniques. In this study, the (7, 4) band was reinvestigated using near-infrared differential velocity modulation laser spectroscopy with higher accuracy and the (7, 2) band was newly observed using visible optical-heterodyne magnetic-rotation velocity-modulation laser spectroscopy (OH-MR-VMLS). N₂⁺ was generated in the AC glow discharge of N2 diluted in He. A large number of lines, namely 272 lines for the (7, 4) band and 216 lines for the (7, 2) band, have allowed us to determine more precise molecular constants for A²Î _u(Ï…'=7) and X²Î£_g⁺ (Ï…"=2,4) states of N₂⁺ than previous study.The CS⁺ cation is assumed to play an important role in the sulfur chemistry in the interstellar medium but its interstellar existence has not yet been identified by the astronomical observation. The perturbation between the vibrational levels of A²Î and X²Î£⁺ states has not been well clarified. In this study, the (5,0) band of...