Microwave Rotational Studies of Small Clusters

211 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1988.The rotational spectra of several small weakly-bonded clusters are examined here. The primary emphasis is on the observation of and results for complexes containing more than two monomer units. Analysis and understanding of these larger clusters regarding structure, dynamics, energetics, and electrical rearrangements in the monomers is shown to be a next step towards bridging the gap between the gas and condensed phases. The clusters, or complexes, have been studied using pulsed-nozzle Fourier transform microwave spectroscopy. The technique as was originally developed has been modified, with these improvements commented on.An extensive study of noble gas-pyridine dimers, Ar-pyridine and Kr-pyridine, is presented in Chapter II. Detailed information regarding the structure of these dimers and the pyridine torsions is derived from the use of isotopic substitution and the nitrogen nuclear quadrupole coupling constants. Also, for the biggest complex to date, the induced $\spƒ$Kr $\chi$'s have been determined, with the field gradients derived for the principal axis system at the Kr nucleus.Chapter III describes the work on the Ar$\sb{\rm m}$HX complexes (m = 1,2,3; X = F,Cl) in focusing on the Ar$\sb2$-HCl trimer and the Ar$\sb3$-HCl tetramer. Analysis of their structures shows the dimer interactions to be maximized with the dimer distances conserved. For the asymmetric tops Ar$\sb2$-HF/Cl, a pseudotriatomic analysis of the centrifugal distortion constants allows semi-quantitative evaluation of the weak intermolecular forces. Comparison with the dimer (Ar-HX, Ar-Ar) force constants shows the values to be reasonable.The results for a second isomeric dimer between CO$\sb2$ and HCN are presented in Chapter IV. The odd formation characteristics of this linear, H-bonded dimer and comparisons with the previously reported T-shaped dimer are discussed.In Chapter V, two X-Y-Z H-bonded trimers are reported on, this serving to illustrate how quickly a system may become complicated by going to larger clusters with more constituent monomers. Also, the use of a dual nozzle source in making the H$\sb3$N-HCN-HF trimer is outlined.Finally, a preliminary analysis on the Ar$\sb2$-HCN trimer is given in Chapter VI. Quite different from the other Ar$\sb2$-HX trimers, it features many of the anomalies observed in Ar-HCN dimer, e.g., large centrifugal distortion and J-dependent $\chi$'s.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD