High resolution UV resonance enhanced two-photon ionization spectroscopy with mass selection of biologically relevant molecules in the gas phase

摘要

The high resolution Doppler-free resonance-enhanced two-photon ionization (R2PI) spectroscopy with mass selection of jet-cooled (2-12 K) molecular species is a powerful experimental method providing comprehensive information on both isolated molecules and molecular clusters. We have demonstrated for the first time that this technique can be applied to large molecules and provides detailed information on their conformational structure. It allows rotationally resolved (FWHM = 70 MHz) spectra of the vibronic bands of the S_1←S_0 electronic transition of the studied molecular systems to be measured. A specially designed computer-assisted fitting routine based on genetic algorithms is used to determine their rotational constants in the ground and excited electronic states, respectively, and the transition moment ratio. To interpret the experimental information and to discriminate and unambiguously assign the observed conformational structures high-level ab initio calculations are performed. Recently we applied the above-described approach to the study of the neurotransmitter molecule, ephedrine. The results elucidate the role of the intramolecular hydrogen bonds stabilizing the respective conformations and affecting their intrinsic properties.