Knowledge Bank

We have measured the Lorentzian linewidths and absolute energy levels of 29 triplet Rydberg states of the $H2$ molecule with quantum numbers $n=11$ to $22,v=1,R=0$ to $3,L=3$. This work provides the first measurements of autoionization rates of triplet nf Rydberg states. Measurements of the absolute energy levels of the Rydberg states relative to the metastable $c(2p)3\Pi u$ state are seven times more precise than the best previous work. An 18eV electron beam excites a collimated $H2$ beam to the metastable $(2p)3\Pi u$ state. Stepwise excitation using two counterpropagating CW single-mode dye laser beams directed perpendicular to the molecular beam path excites the metastable molecule first to an intermediate state, $(3d3\Sigma$ or $3d3\Pi$), then to a triplet of state. While scanning the IR laser used for the last excitation, we detect $H2+$ ions to measure the lineshape and width. In addition we measure the energy to $0.0015cm-1$ of each laser beam (while they are set to the peaks of the transitions) using a travelling-arm interferometer (lambda-meter) referenced to a Zeemanstabilized He-Ne laser. Calculations based on the long range interaction of the Rydberg electron and the polarizability and quadrupole moment of the $H2+$ core predict the energy levels and autoionization $rates.1$ For the $v=1$ Rydberg states we have measured, our data for the widths $(rate=2\pi (width))$ and the energy levels agree well, except for a few well-understood exceptions. Using our measured energy levels we can also derive the ionization potential of the $c(2p)3\Pi u$ metastable state. We obtain the preliminary values: $IP(2p3\Pi u,v=1,N=1,J=2):27137.108(7)cm-1IP(2pu3,v=1,N=2,J=3):27022.078(6)cm-1$ The model predicts that rates for purely rotationally autoionizing Rydberg states ($nf,v=0,R=1$ to $4,L=3$) will be relatively larger; a study of these transitions is in progress.