Q 3. The electronic states of S2 molecule are shown below:
a) What is approximate value from table for equilibrium dissociation energy for electronic ground state?
b) What would happen if molecule was excited to the repulsive 1 II mew state?
c) Which transitions are optically allowed between ground and excited electronic states?
d) Considering color of substance is determined by corresponding complement color that it is absorbing what electronic transition do you think is responsible for yellow color of Sulphur?
a) The presence of S2 is usually monitored by its characteristic strong structured emission spectrum in the ultraviolet, which is due to a transition equivalent to the B3 Σu − ← X3 Σg − Schumann−Runge transition of the isovalent O2 molecule. The threshold photodissociation of S2X3 Σg −(v = 0) is in the 282−266 nm region. Approximate value for the equilibrium dissociation energy for the electronic ground state is 5000 / cm-1.
b) Fine structure branching and angular distributions for photodissociation of S2 occur if the molecule was excited to the repulsive 1Πu state.
c) Transitions for S2 from (X3 Σg −(v = 0), a1 Δg and b1 Σg + ) via the B″3 Πu, B3 Σu − and 1 Πu excited states are optically allowed.
d) Considering that the color of a substance is determined by the corresponding complement color that it is absorbing, the transition from e 1Πg to B 3Πg is responsible for the yellow color of sulphur because transition from 3Πg to 3Πμ, 3Πg to 3Σu, e 1Πg to 3Πμ and 3Σu is forb idden.