Characterisation of the $b^3{\Sigma }^{+},v=0$ State and Its Interaction with the $A^1\Pi$ State in Aluminium Monofluoride

Abstract

Recently, we determined the detailed energy level structure of the $X^1{\Sigma }^{+}$, $A^1\Pi$ and $a^3\Pi$ states of AlF that are relevant to laser cooling and trapping experiments. Here, we investigate the $b^3{\Sigma }^{+},v=0$ state of the AlF molecule. A rotationally-resolved (1+2)-REMPI spectrum of the $b^3{\Sigma }^{+},v^{\prime }=0\leftarrow a^3\Pi ,v^{\prime \prime }=0$ band is presented and the lifetime of the $b^3{\Sigma }^{+},v=0$ state is measured to be 190(2)~ns. Hyperfine-resolved, laser-induced fluorescence spectra of the $b^3{\Sigma }^{+},v^{\prime }=0\leftarrow X^1{\Sigma }^{+},v^{\prime \prime }=1$ and the $b^3{\Sigma }^{+},v^{\prime }=0\leftarrow a^3\Pi ,v^{\prime \prime }=0$ bands are recorded to determine fine- and hyperfine structure parameters. The interaction between the $b^3{\Sigma }^{+},v=0$ and the nearby $A^1\Pi$ state is studied and the magnitude of the spin-orbit coupling between the two electronic states is derived using three independent methods to give a consistent value of 10(1)~cm${}^{-1}$. The triplet character of the $A$ state causes an $A\to a$ loss from the main $A-X$ laser cooling cycle below the 10${}^{-6}$ level.

22 pages, 8 figures

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