The lowres laboratory allows us to record vibrationally resolved spectra to measure the fluorescence lifetime.   Typically, the sample is seeded into He or Ar gas and expanded into a vacuum chamber (10^-5 torr) through a 1 mm diameter orifice pulsed valve (General Valve Series 9), operating at 10 Hz.  One centimeter downstream of the valve, the sample is excited with the second harmonic of a Quanta Ray Nd³⁺: YAG (Model DCR-1A) pumped dye laser (Model PDL-1).  The proper dye is used depending on the desired frequency.  The dye laser output is frequency doubled with an external crystal (KDP or BBO) into the ultraviolet.  From the point of intersection between the supersonic jet and laser, the molecules are excited and the fluorescence is collected with a photomultiplier tube (PMT).  Finally, the collected data is processed by a boxcar integrator (Stanford Research Systems) and digitally recorded with a data acquisition system.

Hires System

The rotationally resolved electronic experiments are performed using a continuous wave (CW) laser spectrometer. Again, the sample is seeded into He or Ar gas, expanded through a quartz nozzle, and probed 15 cm downstream of the nozzle by an Ar+ pumped CW tunable dye laser. Various nozzle diameters are available depending on the needed experimental conditions. The CW laser is operated with the dye of choice. 100-200 μW of UV radiation is produced by intracavity frequency doubling with a BBO or LiIO₃ crystal. Absolute transition frequencies were calibrated by comparing with the I₂ absorption spectrum. Relative frequency calibration was performed using a stabilized etalon with a free spectral range of 299.7520 ± 0.0005 MHz at the fundamental of the dye. The fluorescence excitation spectrum, the iodine absorption spectrum, the relative frequency markers, and the laser output power are simultaneously collected and processed by a data acquisition system.