Rotational spectra and structures of the OC– and H3N–HCN–HF trimers: Coaxial mixing nozzle for reactive species

Abstract

Rotational spectra are reported for several isotopic species of the OC–and H3N–HCN–HF heterotrimers, detected with a pulsed nozzle, Fourier transform, Balle/Flygare microwave spectrometer. Rotational constants for the main isotopic species of the OC trimer are a B0 of 615.574 MHz and DJ of 251 Hz, and for H3N, a symmetric top, a B0 of 1067.161 MHz and DJ and DJK of 0.40 and 63 kHz. Their structures are composites of those reported for the X–HCN and HCN–HF dimers. They are effectively axially symmetric but have some shrinkage from the distances in the dimers. The shrinkages found in r1, the c.m. to c.m. distance for X–HCN are 0.070 and 0.098 Å for X=OC and H3N, respectively, and in r2 for HCN–HF, 0.033 and 0.027 Å. The 14N and H–F hyperfine interactions in OC–HCN–HF are the same as those reported for the HCN–HF dimer. Detection of the X=OC and H3N trimers out of the many species possible required care in their generation. Both were favored by the strongly bonded HCN–HF subunit. The OC–HCN–HF was further enhanced by using a high concentration of CO in the gas expansion. For H3N–HCN–HF a coaxial mixing nozzle was developed to avoid the formation of NH4F(s). The selectivity and simplicity of the nozzle should be helpful in extending the range of species observable with pulsed nozzles.