The Abnormal Absorption Intensity of the C-H Stretching Vibration Band in Chloroform Vapor. I. The CNDO Calculation Involving the 3d Orbitals

By the CNDO calculation involving the 3d orbitals, the infrared absorption intensity of the C–H stretching vibration band in chloroform vapor has been discussed in comparison with those of methyl chloride and methylene chloride. The value of the 3d orbital exponent of the chlorine atom was estimated on the basis of calculations using different values of the 3d orbital exponent on methyl chloride. The absolute intensities of the fundamental and the first overtone bands were calculated from the values of the first and the second derivatives of dipole moments with respect to the normal coordinates. From the results of these calculations, it follows that the electrical properties of the vibrating bond are the most effective factors in bringing about the abnormal absorption intensity of the C–H stretching vibration band in chloroform vapor.