MICROWAVE FOURIER TRANSFORM SPECTROSCOPY

It has been demonstrated that microwave Fourier transform (MWFT) spectroscopy is a sensitive method capable of detecting the rotational spectra of ``nonpolar'' molecules. We have applied MWFT spectroscopy to obtain vibronic ground state and $\\nu_{4}$ exited state rotational spectra of $^{12}CH_{4}. ^{13}CH_{4}, ^{13}CD_{4},$ and $^{28}SiH_{4}$. The tensorial centrifugal distortion constants of the ground vibrational state have been determined and the isotope effects compared to theoretical predictions. From the excited state spectra parameters of the $\\nu_{2}/\\nu_{4}$ dyad Hamiltonian have been determined. In addition, we have observed the pure rotational spectra of allene-1, $1-d_{2}$ and $allene-d_{1}$. A set of rotational constants of $allene-d_{1}$ has been obtained for the first time. The resolving power of MWFT spectroscopy has been demonstrated by resolving the deuterium nuclear quadrupole hyperfine splittings of some rotational transitions of $fluorobenzene-4-d_{1}$.