FTMW spectroscopy of weakly bound complexes, molecules with an internal rotor, and species produced by flash pyrolysis

The thesis has four parts (1) the effect of van der Waals bond on the ring puckering vibration of a four-member ring, (2) the study of a low barrier internal rotation problem, (3) probing a novel method of producing and studying radicals and molecules using flash pyrolysis. Finally, the last chapter of this thesis deals with using a discharge nozzle to characterize unstable molecules and radicals. In addition, chapter one details the motivation behind each of the project.; Argon-chlorocyclobutane is the latest complex studied in a series of molecules involving weakly bound complexes of argon with four member rings. The general goal is to answer the question “is there any effect of the weak van der Waals bond on the ring puckering motion?” The unique position of argon in the present complex highlighted the fact that the averaged position of the argon is close to the van der Waals radius of the β-hydrogen. The structural analysis using rotational constants from six different isotopomers indicates that the effect of the van der Waals bond on the structure of the chlorocyclobutane is minimal. The nuclear quadrupole coupling constant is used to determine the position of the argon independently and proves that the van der Waals bond does not significantly distort the electronic field gradient at the chlorine nucleus. Using the well-determined distortion coefficients for the complex, we will be able to determine the force constants for the interaction between the argon and β-hydrogen.; 2-butynol is a molecule with a low barrier for internal rotation and has been solved to microwave accuracy for the first time. To fit the transitions, a Hamiltonian with higher order terms has been used. Previous molecules with similar barriers have not been fitted to experimental accuracy using the traditional Hamiltonian. The value of V₃ is halved in the new Hamiltonian, while the rest of the analysis indicates that the effect of the higher order term (namely, L_v) is important.; The third chapter involves the study of a novel method of producing radicals, namely flash pyrolysis. This chapter deals with the promises and the problems one faces using this method. A model presented is the increase in rotational temperature leading to a decrease in signal intensity.; The final chapter deals with various studies of unstable radicals/molecules using a discharge nozzle as the source of production. These searches have resulted in many promising but unfinished projects and this chapter summarizes such projects. It is hoped that this summary will be of use to the future members of the research group.