Département de chimie moléculaire

IR-PD vibrational spectroscopy and DFT-based mol. dynamics simulations are combined in order to unravel the structures of M+(APE)(H2O)0-1 ionic clusters (M = Na, K), where APE (2-amino-1-Ph ethanol) is commonly used as an analog for the noradrenaline neurotransmitter. The strength of the synergy between expts. and simulations presented here is that DFT-MD provides anharmonic vibrational spectra that unambiguously help assign the ionic clusters structures. Depending on the interacting cation, we have found that the lowest energy conformers of K+(APE)(H2O)0-1 clusters are formed, while the lowest energy conformers of Na+(APE)(H2O)0-1 clusters can only be obsd. through water loss channel (i.e. without argon tagged to the clusters). Trapping of higher energy conformers is obsd. when the argon loss channel is recorded in the expt. This has been rationalized by transition state energies. The dynamical anharmonic vibrational spectra unambiguously provide the prominent OH stretch due to the OH···NH2 H-bond, within 10 cm-1 of the expt., hence reproducing the 240-300 cm-1 red-shift (depending on the interacting cation) from bare neutral APE. When this H-bond is not present, the dynamical anharmonic spectra provide the water O-H stretches as well as the rotational motion of the water mol. at finite temp., as obsd. in the expt. [on SciFinder(R)]