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

Abstract

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(1Δu) 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(1Δu) and 3A2(3Δu) 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(3Δu) state. The fluorescence decays of single Zeeman components were observed to be single exponential. The lifetimes of the perturbing 3A2(3Δu) levels were determined by deperturbation analysis. Triplet-triplet 3A2(3Δu) → 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(1Δu) and 3A2(3Δu) states is enhanced by the magnetic field.