Br 2 (B
3 P u (0
+
) * C
1 P u (1)) gyroscopic predissociation. The dip and decrease of the
k v = f(v) observed (Fig. 4.23c) is a consequence of the dephasing of the vibrational
wave functions and (or) their different periods.
One must be aware that the separation of the concepts of adiabatic or diabatic
PECs is arbitrary; these coupling limits are applicable if the probability P 1,2
(Figs. 3.16, 3.17) is close to 1 or 0. Otherwise (interaction of an intermediate force),
it is impossible to draw a boundary between these couplings.
Figure 4.22d shows the case of a ‘strong’ interaction of the adiabatic bound and
repulsive states, In this case, the probability of a nonadiabatic transition from point
a to point b is much less than from point a to point d and, accordingly, from point
c to point d is much smaller than from point c to point b. The AB* states at energies
greater than the corresponding barrier to the PEC of AB* practically belong to the
continuous energy spectrum.
Often there is a case of interaction of states of the same type of symmetry of
intermediate strength. Figure 4.22d shows the PECs of the IBr(B0
+ and B
0 0
+ ) states,
which are formed as a result of the interaction of the bound and repulsive 0
+ states.
The matrix element of the interaction of these states is not too large, and in the
absorption spectrum at an energy larger than the corresponding intersection point,
two progressions of the bands are observed, corresponding to transitions to the
B and B
0 states, i.e., the B state in this energy region does not belong to the
continuous energy spectrum. Accordingly, a transition to a part of the PEC that is
above the dissociation threshold of B state with a probability greater than 0.62 leads
to a nonadiabatic transition between the B and B
0 states. One can populate the
B state rovibronic level, and observe luminescence from state B
0 and vice versa
[27].
4.7.2 Predissociation of Polyatomic Molecules
The predissociation of polyatomic molecules is discussed in detail in Herzberg’s
monograph [10]. Therefore, in this book, the author will note only the following.
The possibilities of predissociation in polyatomic molecules are much larger than in
diatomic ones: this is a direct consequence of the multidimensionality of PESs, in
particular, the increase in the lifetime of excited states due to the coupling of
various vibrational modes and dimensions of the PES interaction regions. The
motion of an image point in the predissociation is described as follows: when a PES
quasi-intersection or intersection region passes, an image point with probability
P jumps from one PES to another, so that when exiting this area, there will already
be two trajectories, one on the original PES, the other on the ‘new’. Further, the
system is described by adiabatic motion until one of these trajectories comes up
again to this ‘interesting’ area and again forks, etc.
140
4 Photolysis of Free Molecules
3 P u (0
+
) * C
1 P u (1)) gyroscopic predissociation. The dip and decrease of the
k v = f(v) observed (Fig. 4.23c) is a consequence of the dephasing of the vibrational
wave functions and (or) their different periods.
One must be aware that the separation of the concepts of adiabatic or diabatic
PECs is arbitrary; these coupling limits are applicable if the probability P 1,2
(Figs. 3.16, 3.17) is close to 1 or 0. Otherwise (interaction of an intermediate force),
it is impossible to draw a boundary between these couplings.
Figure 4.22d shows the case of a ‘strong’ interaction of the adiabatic bound and
repulsive states, In this case, the probability of a nonadiabatic transition from point
a to point b is much less than from point a to point d and, accordingly, from point
c to point d is much smaller than from point c to point b. The AB* states at energies
greater than the corresponding barrier to the PEC of AB* practically belong to the
continuous energy spectrum.
Often there is a case of interaction of states of the same type of symmetry of
intermediate strength. Figure 4.22d shows the PECs of the IBr(B0
+ and B
0 0
+ ) states,
which are formed as a result of the interaction of the bound and repulsive 0
+ states.
The matrix element of the interaction of these states is not too large, and in the
absorption spectrum at an energy larger than the corresponding intersection point,
two progressions of the bands are observed, corresponding to transitions to the
B and B
0 states, i.e., the B state in this energy region does not belong to the
continuous energy spectrum. Accordingly, a transition to a part of the PEC that is
above the dissociation threshold of B state with a probability greater than 0.62 leads
to a nonadiabatic transition between the B and B
0 states. One can populate the
B state rovibronic level, and observe luminescence from state B
0 and vice versa
[27].
4.7.2 Predissociation of Polyatomic Molecules
The predissociation of polyatomic molecules is discussed in detail in Herzberg’s
monograph [10]. Therefore, in this book, the author will note only the following.
The possibilities of predissociation in polyatomic molecules are much larger than in
diatomic ones: this is a direct consequence of the multidimensionality of PESs, in
particular, the increase in the lifetime of excited states due to the coupling of
various vibrational modes and dimensions of the PES interaction regions. The
motion of an image point in the predissociation is described as follows: when a PES
quasi-intersection or intersection region passes, an image point with probability
P jumps from one PES to another, so that when exiting this area, there will already
be two trajectories, one on the original PES, the other on the ‘new’. Further, the
system is described by adiabatic motion until one of these trajectories comes up
again to this ‘interesting’ area and again forks, etc.
140
4 Photolysis of Free Molecules