Journal of Physical Chemistry A, Vol.110, No.46, 12597-12602, 2006
IR spectroscopy of hydrogen-bonded 2-fluoropyridine-methanol clusters
The electronic and infrared spectra of 2-fluoropyridine-methanol clusters were observed in a supersonic free jet. The structure of hydrogen-bonded clusters of 2-fluoropyridine with methanol was studied on the basis of the molecular orbital calculations. The IR spectra of 2-fluoropyridine-(CH3OH)(n)(n = 1-3) clusters were observed with a fluorescence-detected infrared depletion (FDIR) technique in the OH and CH stretching vibrational regions. The structures of the clusters are similar to those observed for 2-fluoropyridine-(H2O)(n)- (n = 1-3) clusters. The existence of weak hydrogen bond interaction through aromatic hydrogen was observed in the IR spectra. The theoretical calculation also supports the result. The vibrational frequencies of CH bonds in CH3 group are affected by hydrogen bond formation although these bonds do not directly relate to the hydrogen bond interaction. The B3LYP/6-311++G(d, p) calculations reproduce well the vibrational frequency of the hydrogen-bonded OH stretching vibrations. However, the calculated frequency of CH stretching vibration could not reproduce the IR spectra because of anharmonic interaction with closely lying overtone or combination bands for v(3) and v(9) vibrations. The vibrational shift of v(2) vibration is reproduced well with molecular orbital calculations. The calculation also shows that the frequency shift of v(2) vibration is closely related to the CH bond length at the trans position against the OH bond in hydrogen-bonded methanol.