Book Description

"Our group was the first to extend studies of the rotational spectra of small and fundamental gas-phase molecules from the microwave into first the millimeter-wave and subsequently the submillimeter-wave region of the spectrum(King & Gordy 1953;Helmingeret al. 1970,1983).A bibliography of the many molecules studied in the laboratory, consisting of over400 papers, is available upon request. The results presented in these papers provide the basis for the identification of a significant fraction of the interstellar spectral lines. For interstellar molecules previously detected at lower frequencies, our submillimeter-wave spectra provide the opportunity for additional study of these species under warmer conditions. For the duration of this proposal and previously, we have concentrated on those molecules with the Largest number of interstellar spectral lines. These species are so-called internal rotors, in which one portion of the molecule(normally a methyl (CH3) group) undergoes a hindered rotational motion with respect to the other portion of the molecule. The hindered rotational motion, known as torsion, leads to quantized states typically separated by 50-100 K and labeled with a quantum number vt= 0,1,2 ... For the three-fold case, each torsional state is also split into two substates-designated A and E. The existence of these extra states compared with normal molecules is of great use for probing warm regions with temperatures too low to excite normal vibrations but higher than the ambient interstellar medium. Strong interactions between torsional and rotational motion, however, make the spectra of some internal rotors quite complex and, for many years, it was very difficult if not impossible to analyze their spectra to microwave accuracy. Without such a detailed analysis, it is not possible to predict the frequencies of the many lines not measured in the laboratory with sufficient precision for use by radio astronomers, nor to determine intensities."--Page 2.