Absolute absorption intensities were calculated for the symmetry dipole forbidden n --> pi* 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 --> pi* transition in formaldehyde presenting an excellent agreement with the experimental results.