Two-photon Doppler-free ultraviolet laser spectroscopy on sulphur atoms.

The 3p⁴³P_J–3p³4p³P_J transition in the sulphur atom is investigated in a precision two-photon excitation scheme under Doppler-free and collision-free circumstances yielding an absolute accuracy of 0.0009 cm⁻¹, using a narrowband pulsed laser. This verifies and improves the level separations between amply studied odd parity levels with even parity levels in S I. An improved value for the ³P₂–³P₁ ground state fine structure splitting is determined at 396.0564 (7) cm⁻¹. A ³⁴S–³²S atomic isotope shift was measured from combining time-of-flight mass spectrometry with laser spectroscopy. [ABSTRACT FROM AUTHOR]