Photofragment Spectrometer

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Abstract
An apparatus for photofragment spectroscopy, a new type of molecular spectroscopy for dissociative electronic states, is described. Inside an ultrahigh vacuum system, a molecular beam is crossed by pulses of polarized light (from a theta‐pinch discharge or from various lasers, including ruby, second harmonic ruby, second harmonic neodymium‐glass, and laser pumped tunable dye) and the recoiling photodissociation fragments are detected by a quadrupole mass spectrometer a few centimeters away. The data are collected and analyzed by an on‐line time shared computer and presented on a computer driven oscilloscope display as plots of number of fragments detected per microsecond vs time after the laser pulse. Parameters such as photon energy, photon flux, fragment mass, and fragment laboratory recoil angle with respect to the electric vector of the light can be varied to obtain a multidimensional spectrum. This spectrum, the probability of photodissociation as a function of photon energy and flux and of fragment mass, center‐of‐mass translational energy, and center‐of‐mass angle of recoil, may be used to study many aspects of molecular states.

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