The compound converts to benzene with a chemical half-life of approximately 10 days . This symmetry-forbidden transition is believed to take place through a diradical intermediate.
12.
Semi-forbidden transitions ( resulting in so-called intercombination lines ) are electric dipole ( E1 ) transitions for which the selection rule that the spin does not change is violated.
13.
Difference bands are seldom observed in conventional vibrational spectra, because they are forbidden transitions according to harmonic selection rules, and because populations of vibrationally excited states tend to be quite low.
14.
The expression " forbidden transitions " is often used; this does not mean that these transitions cannot occur, only that they are " electric-dipole-forbidden ".
15.
The first excited state ( a 1 ? ) has a long lifetime because there is a spin-forbidden transition between it and the electronic ground state ( X 3 ? " ).
16.
The low probability for collisions in the nebula made it impossible for the oxygen to get from the excited stated to the ground state and so the forbidden transitions were the main path for the relaxation.
17.
The only things I found missing was a density of oxygen in its liquid and solid states, and mention of Oxygen's ( forbidden transition ) role in Nebulium, as explained by I . S . Bowen.
18.
The long half life of this primordial radioisotope is caused by a highly spin-forbidden transition : 40 K has a nuclear spin of 4, while both of its decay daughters are even-even isotopes with spins of 0.
19.
More precisely, there is a certain probability that such an excited entity will make a forbidden transition to a lower energy state per unit time; by definition, this probability is much lower than that for any transition permitted or allowed by the selection rules.
20.
Nevertheless, most forbidden transitions are only relatively unlikely : states that can only decay in this way ( so-called meta-stable states ) usually have lifetimes on the order milliseconds to seconds, compared to less than a microsecond for decay via permitted transitions.
