Knowledge Bank

We have recently acquired a high resolution Fourier transform spectromerter with the primary interest of studying molecular emission spectra, particularly in the infrared region. If one wished to design a molecule for testing and optimizing the performance of a spectrometer over a wide spectral region, one could hardly conceive of a better one than the CN radical. CN is probably the most studied diatomic free radical, and its properties have been previously investigated, including a recent observation by Vaida and co-$workers.1$ The CN radical was produced in a corona discharge of acetonitrile entrained in an inert carrier gas, argon or helium, and expanded through a 0.2 mm nozzle. Stagnation pressures of 10-20 psi were used. Under these conditions the pressures in the chamber during operation were about 0.5 - 1 Torr. The nozzle was formed from a thick walled glass capillary, narrowed at one end to provide the desired size orifice. The anode consisted of a sharpened 2 mm diameter stainless steel wire. The metal tubing connecting the vacuum chamber to the pump, which was held at ground potential, served as the cathode. The anode was held at 3000 V with a discharge current of typically 4-5 mA. Vibrational levels of the B - X transition have been observed up to $v=14$ and rotational constants have been determined. The 0 - 0 transition shows evidence of a dual temperature, that most likely corresponds to two distinct formation mechanisms of the electronically excited B state molecules. Vibrational levels of the A - X transition have also been observed up to v = 16 and the $\Delta v=-1,-2$, and $-$3 bands extend well into the near IR down to 3000 $cm-1$. Attempts to observe the X state vibrational emission are ongoing.