Knowledge Bank

Hydrogen clusters are produced in a supersonic expansion and are subsequently doped with K atoms by passing the beam through a pick-up cell conntaining K vapour at a pressure of about $10-2$ Pa. Optical $42P32,frac32\leftarrow 42S12$ spectra for K atoms are obtained in two different ways: a) by Laser Induced Fluorescence (LIF) b) by measuring the Beam Depletion (BD) induced by the laser using a hot wire surface ionization detector located downstream of the LIF collector For hydrogen clusters the LIF spectra are two orders of magnitude lower in intensity as compared to those obtained using He clusters, due to quenching. The LIF spectra consist of several narrow features near the gas phase potassium doublet and a second series of very broad features located about $300-600cm-1$ to the blue. The BD spectrum shows surprising differences from the LIF. The blue-shifted features are still preasent, but most of the absorption is now located under a prominent envelope (about $200cm-1$ broad) centered on the gas phase doublet. These differences will be discussed at the meeting.