Conformational Structure Determination of Biomolecules in the Gas Phase using Broadband Fourier Transform Microwave Spectroscopy

We have recently developed a true broadband Fourier transform microwave (FTMW) spectrometer that obtains the rotational spectrum in the 7.5 -- 18.5 GHz range with 50 kHz resolution for each individual valve pulse in a molecular beam spectrometer. The ability to observe an 11 GHz broad rotational spectrum for each valve pulse is particularly useful for experiments where the molecular beam source conditions require optimization and in cases where the biological sample decomposes over a time scale of a few minutes. The high resolution of the measurement makes it possible to unravel the conformational complexity of gas phase biomolecules. Conformational assignments of the pure rotational spectrum of p-methoxyphenethylamine (MPEA) will be presented to illustrate the capabilities of the spectrometer. The spectrometer can also be employed in laser-FTMW double-resonance experiments where the conformational assignments in the pure rotational spectrum are used to automatically assign absorption features in either vibrational or electronic spectra.