RESUMO
For isolated fluoroform (F(3)CH) molecules adsorbed on a hexagonal ice (0001) surface the properties of blue- and red-shifting hydrogen bonds were studied using static density functional theory (DFT) calculations and Car-Parrinello molecular dynamics (CP-MD) simulations. A systematic search by starting from many initial configurations was performed to determine the lowest-energy structures of F(3)CH on the ice surface, and for the optimized geometries the vibrational frequencies were calculated. The local minima structures are analyzed in terms of their coordination to the surface, with special focus on identifying blue-shifting hydrogen bonds via their spectroscopic signature of an increased frequency of the C-H fundamental stretching vibration. Subsequently, by CP-MD simulations the stability of the lowest-energy configurations at finite temperatures was verified and possible transformation pathways connecting the local minima structures were explored.
RESUMO
Fluoroform, as confirmed by both experimental and theoretical studies, can participate in improper H-bond formation, which is characterized by a noticeable increase in the fundamental stretching frequency nu(C-H) (so-called blue frequency shift), an irregular change of its integral intensity, and a C-H bond contraction. A Car-Parrinello molecular dynamics simulation was performed for a complex formed by fluoroform (F3CH) and deuterated methyl fluoride (FCD3) in liquid nitrogen. Vibrational analysis based on the Fourier transform of the dipole moment autocorrelation function reproduces the blue shift of the fundamental stretching frequency nu(C-H) and the decrease in the integral intensity. The dynamic contraction of the C-H bond is also predicted. The stoichiometry of the solvated, blue-shifted complexes and their residence times are examined.
