Doppler-free high resolution spectroscopy of carbon disulphide and the effects of a magnetic field

A single-mode autoscan laser spectrometer operating in the ultraviolet in combination with a collimated molecular beam was used to measure high resolution fluorescence excitation spectra of the CS₂ V ¹B₂ ← X ¹Σ⁺ _g transition under collision-free conditions, and the effects of a magnetic field were measured. Rotational and vibrational levels were fully resolved, and Zeeman splittings were observed in many of the perturbed lines. The Zeeman interaction was observed to induce new perturbation, which induces new transitions, level splitting, and energy shift. When the magnetic field strength was changed, the magnitude of the interaction, which was observed in the absence of a magnetic field, changed dramatically depending on the energy shifts of the Zeeman components. It is shown that the V ¹B₂(¹Δ_u) state is mixed with the B₂(³A₂) component by first-order spin-orbit interaction, and through the mixed component, the Zeeman interaction between the V ¹B₂(¹Δ_u) and ³A₂(³Δ_u) states is induced. Large Zeeman splittings were observed for most of the background lines of weak intensity, and this demonstrates that the background levels are levels of the ³A₂(³Δ_u) state. The fluorescence decays of single Zeeman components were observed to be single exponential. The lifetimes of the perturbing ³A₂(³Δ_u) levels were determined by deperturbation analysis. Triplet-triplet ³A₂(³Δ_u) → ³B₂(³Σ⁺ _u) emission was confirmed. It was demonstrated that the quenching of the V ¹B₂ → X ¹Σ⁺ _g fluorescence by a magnetic field was caused by mixing of the ³A₂ state with the V ¹B₂ state and the resulting increase of triplet-triplet emission. In a time-dependent picture, the intersystem crossing from the ¹B₂(¹Δ_u) and ³A₂(³Δ_u) states is enhanced by the magnetic field.