Direct Lifetime Measurement of Laser-Excitedn=3Levels in Para-H2

This paper reports measurements of the lifetimes of fourteen levels in the $3s$, $3d$ complex of para-${\mathrm{H}}_2$ by a delayed coincidence method. A collimated beam of metastable hydrogen molecules was selectively excited by light pulses from a cw dye laser and fluorescent radiation was detected by a vacuum ultraviolet photomultiplier. The observed lifetimes range from 11.1 to 48.8 nsec. Similar methods can be used to determine the structure and lifetimes in other excited states of ${\mathrm{H}}_2$ and in a variety of other systems.