Intensity of the n→π∗ symmetry-forbidden electronic transition in acetone by direct vibronic coupling mechanism

Absolute absorption intensities were calculated for the symmetry dipole forbidden n→π∗ transition in acetone. An analysis of the distribution per normal modes is performed and the results are compared with a recent calculation. Vibronic coupling mechanism is taken into account in a way that is different from the traditional Herzberg–Teller perturbation approach. In the present method the electronic transition moment is directly expanded in power series of the vibration normal coordinates. This approach was recently used for the equivalent n→π∗ transition in formaldehyde presenting an excellent agreement with the experimental results.