Knowledge Bank

We have been experimenting with nozzle design to extend the utility of the Flygare- Balle spectrometer1 In observing rotational spectra of transient species. The spectrometer traditionally uses a single, pulsed nozzle from which a premixed gas expands into the Fabry-Perot cavity. We have now tried several modifications in which gases from two different sources are mixed in the expansion region, with a much shortened, adjustable contact time. A coaxial source is useful in avoiding unwanted reactions. It consists of a fine inner tube with a continuous (cw) flow of one gas (mixture) and an outer tube generating a pulsed beam of another. Mixing $NH3$ and HX gas ordinarily produces a cloud of solid NH4X particles. However, the rotational spectrum of vapor over heated solid $NH4CI(450K)$ has recently shown it to be a hydrogen bonded $NH3-HCl$ diner. We have observed rotational transitions of the latter at much larger S/N using a coaxial nozzle at ambient temperature with 5*** HCl/He in the ow Inner tube and $0.3\ast NH3/Ar$ in the pulsed outer tube. In addition, for the first time, the microwave spectrum of the hydrogen bonded, linear trimer. NH3-HCN-HF, has been observed. Preliminary results for $Bo$ and $D1$ are $1067.09MHz$ and-$0.4KHz$. For it, 5* HF/He was used in the inner tube and $0.3\ast NH3\ast HCN/Ar$ in the outer. Further extensions and applications are in progress.