Knowledge Bank

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 $\mathrm{<mrow\; data-mjx-texclass="ORD">12</mrow>}CH4.13CH4,13CD4,$ and $\mathrm{<mrow\; data-mjx-texclass="ORD">28</mrow>}SiH4$. 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, $1-d2$ and $allene-d1$. A set of rotational constants of $allene-d1$ 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 $fluorobenzene-4-d1$.