Dipole Moment Derivatives of Free And Hydrogen Bonded O-H Bond of Methanol

Infrared intensities of fundamental and first overtone bands of 0-H stretching mode of methanol are reported ina few hydrogen bonding solvents. From these intensity data the first and second dipole moment derivatives have been computed. It is noticed that the intensity of the fundamental band increases appreciably on hydrogen bonding whereas the first overtone does not show much change in intensity. Two sets of dipole moment derivatives obtained from ++ and + - combinations of the transition moment matrix elements rq and R2Q are considered, the values for -- and -+ combinations are equal in magnitude to those of + + and +- combinations respectively and opposite in signs it is observed that in all the cases studied both the dipole moment derivatives of 0-H bond increase on hydrogen bonding. It is shown that with an increase in the values of both the dipole moment derivatives not only one can explain an appreciable increase in the intensity of the fundamental band with little or no increase in the intensity of the overtone band but one can even explain the decrease in the overtone band intensity because of the inclusion of mechanical anharrnonicity terms in the transition moment expressions. © 1981 by Marcel Dekker, Inc.