SF: Stabilizing Transient Ions in Helium Nanodroplets.

There are myriad ions that are deemed too short-lived to be experimentally accessible. One of them is SF. It has never been observed, although not for lack of trying. We demonstrate that long-lived SF can be formed by doping charged helium nanodroplets (HNDs) with sulfur hexafluoride; excess helium is then gently stripped from the doped HNDs by collisions with helium gas. The ion is identified by high-resolution mass spectrometry (resolution /Δ = 15000), the close agreement between the expected and observed yield of ions that contain minor sulfur isotopes, and collision-induced dissociation in which mass-selected HeSF ions collide with helium gas. Under optimized conditions, the yield of SF exceeds that of SF. The procedure is versatile and suitable for stabilizing many other transient molecular ions.