multiplet turned out to be populated, namely, B
2 P 3/2 ,v B = 0,J B = 10.5, and B
2 P 3/2 ,
v B = 3,J B = 17.5, and a broad set of rotational levels of NO(b
4 R
−
,v b = 3–5).
Let us now consider the B state. Everything is very similar to the case described
in the framework of the gateway model. The analysis of the obtained and published
data, as well as the study of the lifetimes of the NO(B
2 P 3/2 ,v B = 0,J B = 10.5, and
B
2 P 3/2 ,v B = 3,J B = 17.5) clarified the following picture:
Unperturbed rovibronic states NO(B
2 P 3/2 ,v B = 0,J B = 10.5 and a
4 P 5/2 ,v a = 8,
J a = 10.5, as well as NO(B
2 P 1/2 ,v B = 3,J B = 17.5) and a
4 P 5/2 ,v a = 12,J a = 17.5)
are randomly in the exact resonance, DE % 10
–4 cm
−1 . The electronic matrix element of the interaction of these states A el is small since the spin momenta of these
states are different and the nuclei in the molecule are relatively light: A el % 50 cm
−1 .
Besides, the overlap integrals of the vibrational wave functions of the B,0 * a,8
and B,3 * a,12 states are of the order of 5 10
–5 (Frank–Condon factors of the order
of 2 10
–9 ). Consequently, the matrix element of their interaction is negligible, of the
order of nÁ10
–3 , and resonance of the order of 10
–3 cm
−1 is required for mixing
these levels of the B, and a states. A stream of NO molecules flies onto the target, in
which a huge number of the NO(a) metastable state rovibronic levels are, including
those in the vicinity of v a = 8,J a = 10.5 and v a = 12,J a = 17.5. The latter are just
absent, since they are mixed with the v B = 0,J B = 10.5 and v B = 3,J B = 17.5 levels
and have decayed in radiation transitions along the way to the observation zone.
What will happen if molecules excited in this way collide with a target species?
Collisions lead to T-R (from bottom to top) and R-T (from top to bottom) to
populate the v a = 8,J a = 10.5 and v a = 12,J a = 17.5 levels. Then spontaneous
transitions to the NO(B
2 P 3/2 ,v B = 0,J B = 10.5 and NO(B
2 P 1/2 ,v B = 3,J B = 17.5)
states occur, followed by optical transitions, which we discussed above. Since the
exact (< 10
–3 cm
−1 ) resonance and the fulfillment of the selection rule J 1 = J 2 takes
place only for the levels indicated above, only they find themselves in the radiation.
It must be borne in mind, of course, that a complex is formed during a collision,
and as a result, DE, and the matrix element of the interaction of the complex states
correlating with the rovibronic levels depend on R NOÃ...M . But still, it remains very
small, since on the asymptote, it is negligible (< 10
–3 cm
−1 ). The gateway model is
applicable if V 1,2 < 1 cm
−1 . Here this inequality holds.
Other perturbation facilitated processes. What will happen if V 1,2 > 1 cm
−1 ? In
the case of the NO(B,v B * a,v a ), mixing this can happen if NO collides with a heavy
atom, like Xe, or with a paramagnetic molecule such as NO or O 2 , for example. In
the general case, this can be, if either the electronic part of the matrix elements of the
interaction of states in a free molecule, or/and the overlap integrals are sufficiently
large. The gateway model is not applicable in this case, and one must consider the
processes already within the complex. Such effects were observed in [24].
In particular, when M = Xe, O 2 , and especially NO, the NO(a,v a )
… M complex is
formed, the matrix elements of the interaction in which are so large that inequality
(5.5.6) is certainly not satisfied. The interaction of a heavy or paramagnetic species
with NO leads to the fact that the spin momentum conservation rule is violated (Xe),
or the total spin of the colliding partners is retained, due to the nonzero M spin
momentum, while that of NO changes. One way or another, the requirements for
5.5 Collision-Induced Nonadiabatic Transitions
173
2 P 3/2 ,v B = 0,J B = 10.5, and B
2 P 3/2 ,
v B = 3,J B = 17.5, and a broad set of rotational levels of NO(b
4 R
−
,v b = 3–5).
Let us now consider the B state. Everything is very similar to the case described
in the framework of the gateway model. The analysis of the obtained and published
data, as well as the study of the lifetimes of the NO(B
2 P 3/2 ,v B = 0,J B = 10.5, and
B
2 P 3/2 ,v B = 3,J B = 17.5) clarified the following picture:
Unperturbed rovibronic states NO(B
2 P 3/2 ,v B = 0,J B = 10.5 and a
4 P 5/2 ,v a = 8,
J a = 10.5, as well as NO(B
2 P 1/2 ,v B = 3,J B = 17.5) and a
4 P 5/2 ,v a = 12,J a = 17.5)
are randomly in the exact resonance, DE % 10
–4 cm
−1 . The electronic matrix element of the interaction of these states A el is small since the spin momenta of these
states are different and the nuclei in the molecule are relatively light: A el % 50 cm
−1 .
Besides, the overlap integrals of the vibrational wave functions of the B,0 * a,8
and B,3 * a,12 states are of the order of 5 10
–5 (Frank–Condon factors of the order
of 2 10
–9 ). Consequently, the matrix element of their interaction is negligible, of the
order of nÁ10
–3 , and resonance of the order of 10
–3 cm
−1 is required for mixing
these levels of the B, and a states. A stream of NO molecules flies onto the target, in
which a huge number of the NO(a) metastable state rovibronic levels are, including
those in the vicinity of v a = 8,J a = 10.5 and v a = 12,J a = 17.5. The latter are just
absent, since they are mixed with the v B = 0,J B = 10.5 and v B = 3,J B = 17.5 levels
and have decayed in radiation transitions along the way to the observation zone.
What will happen if molecules excited in this way collide with a target species?
Collisions lead to T-R (from bottom to top) and R-T (from top to bottom) to
populate the v a = 8,J a = 10.5 and v a = 12,J a = 17.5 levels. Then spontaneous
transitions to the NO(B
2 P 3/2 ,v B = 0,J B = 10.5 and NO(B
2 P 1/2 ,v B = 3,J B = 17.5)
states occur, followed by optical transitions, which we discussed above. Since the
exact (< 10
–3 cm
−1 ) resonance and the fulfillment of the selection rule J 1 = J 2 takes
place only for the levels indicated above, only they find themselves in the radiation.
It must be borne in mind, of course, that a complex is formed during a collision,
and as a result, DE, and the matrix element of the interaction of the complex states
correlating with the rovibronic levels depend on R NOÃ...M . But still, it remains very
small, since on the asymptote, it is negligible (< 10
–3 cm
−1 ). The gateway model is
applicable if V 1,2 < 1 cm
−1 . Here this inequality holds.
Other perturbation facilitated processes. What will happen if V 1,2 > 1 cm
−1 ? In
the case of the NO(B,v B * a,v a ), mixing this can happen if NO collides with a heavy
atom, like Xe, or with a paramagnetic molecule such as NO or O 2 , for example. In
the general case, this can be, if either the electronic part of the matrix elements of the
interaction of states in a free molecule, or/and the overlap integrals are sufficiently
large. The gateway model is not applicable in this case, and one must consider the
processes already within the complex. Such effects were observed in [24].
In particular, when M = Xe, O 2 , and especially NO, the NO(a,v a )
… M complex is
formed, the matrix elements of the interaction in which are so large that inequality
(5.5.6) is certainly not satisfied. The interaction of a heavy or paramagnetic species
with NO leads to the fact that the spin momentum conservation rule is violated (Xe),
or the total spin of the colliding partners is retained, due to the nonzero M spin
momentum, while that of NO changes. One way or another, the requirements for
5.5 Collision-Induced Nonadiabatic Transitions
173