Question

What does the “vertical transition” in electronic spectroscopy (UV-Vis) mean and what is the

rationale for this approximation? Please explain and show all work.

Answer 1

1)

An absorption leads to a higher energy state, fluorescence leads to a lower energy state, and the shift in nuclear coordinates between the ground and excited state is indicative of a new equilibrium position for nuclear interaction potenial. The fact is that the fluorescence arrow is shorter than the absorption indicates that it has less energy, or that its wavelength is longer. This change in vibration is maintained during a state termed the rapid electronic excitation. The resulting Coulombic forces produce an equilibrium for the nuclei termed a turning point. The turning point can be mapped by drawing a vertical line from the minimum of the lower curve to the intersection of the higher electronic state. This procedure is termed a vertical transition.

2)

Vertical transition explains the relative intensities of vibronic transitions by relating the probablity of a vibrational transition to the overlap of the vibrational wave functions. It states the probability of a vibrational transition occurring. In this case, the nuclei are considered "fixed" during electronic transitions. Thus, electronic transitions can be considered vertical transitions on electronic potential energy curves.

3)

The vertica transition is referred by the name of Franck Condon Principle.