V-T processes, there can be others, in particular, those discussed below. So, the data
obtained in this way are nothing more than a subject for the start of a serious study.
It should be said that there is currently no theory with which you could calculate the
vibrational relaxation constants at intermediate levels. You can get them only in the
experiment by populating a single level and examining the dependence of the
population of this and other levels on the M pressure. But in the general case, this
also does not guarantee your success, since in addition to vibrational relaxation, a
bunch of other collisional and spontaneous processes can take place. Numerical
modeling can be useful for establishing their mechanism and kinetics. But even in
this case, with success, one must say: ‘We were able to describe the dependence
observed in the experiment consistently.’
The mechanism of vibrational relaxation is interesting if the vibrational excitation energy E, which transforms into kinetic energy in a collision, is close to kT.
This mechanism is realized at the vibrational relaxation of the I 2 (B0
þ
u ) molecule
[20]. In this case, the highest probability of relaxation is observed if the collision
time t coll is equal to the oscillation period T v . The vibrational relaxation constant can
be equal to k gk in this case.
In general, the following pattern can be traced. Rate of V-T processes:
• - increases with increasing of collision partner reduced mass l if the energy
taken away in a collision DE << kT;
• falls if DE >> kT;
• if DE = kT, then it is maximum when t coll = T v for a given l.
5.4 The Influence of Nonadiabatic Effects
on the Vibrational Relaxation Rate
Consider the collision of NO molecule in the ground state with He atom, for
example. It is known that the ground state of NO(X
2 P 1/2,3/2 ) can be considered as
degenerate. Whether it is degenerate or not, it should be spoken, bearing in mind the
energy scale. This state is non-totally symmetric both in the orbital function and in
the spin: K = 1, S = 1/2. Therefore, there are two X components of this state:
X = 1/2, 3/2. The splitting between them is very small, 0.0148 eV * ½ kT, and it
can be neglected in many cases, i.e., consider the ground state as degenerate.
However, this cannot be done a priori, considering vibrational relaxation within the
NO ground state. Here we must take into account that in fact, we deal with two
states NO − X
2 P 1/2 and X
2 P 3/2 , whose E values differ by 0.0148 eV, and two
PECs correlated in the zero approximation to the of N(
4 S) + O(
3 P) limit. In the
zeroth approximation since there is a fine structure of the term O(
3 P J ), J = 2, 1, 0,
splitting DE 2-0 % 0.03 eV (see [8] and references). If we take this effect into
account, the picture will be even more complicated, so let us stop for now.
5.3 Vibrational Energy Transfer
165
obtained in this way are nothing more than a subject for the start of a serious study.
It should be said that there is currently no theory with which you could calculate the
vibrational relaxation constants at intermediate levels. You can get them only in the
experiment by populating a single level and examining the dependence of the
population of this and other levels on the M pressure. But in the general case, this
also does not guarantee your success, since in addition to vibrational relaxation, a
bunch of other collisional and spontaneous processes can take place. Numerical
modeling can be useful for establishing their mechanism and kinetics. But even in
this case, with success, one must say: ‘We were able to describe the dependence
observed in the experiment consistently.’
The mechanism of vibrational relaxation is interesting if the vibrational excitation energy E, which transforms into kinetic energy in a collision, is close to kT.
This mechanism is realized at the vibrational relaxation of the I 2 (B0
þ
u ) molecule
[20]. In this case, the highest probability of relaxation is observed if the collision
time t coll is equal to the oscillation period T v . The vibrational relaxation constant can
be equal to k gk in this case.
In general, the following pattern can be traced. Rate of V-T processes:
• - increases with increasing of collision partner reduced mass l if the energy
taken away in a collision DE << kT;
• falls if DE >> kT;
• if DE = kT, then it is maximum when t coll = T v for a given l.
5.4 The Influence of Nonadiabatic Effects
on the Vibrational Relaxation Rate
Consider the collision of NO molecule in the ground state with He atom, for
example. It is known that the ground state of NO(X
2 P 1/2,3/2 ) can be considered as
degenerate. Whether it is degenerate or not, it should be spoken, bearing in mind the
energy scale. This state is non-totally symmetric both in the orbital function and in
the spin: K = 1, S = 1/2. Therefore, there are two X components of this state:
X = 1/2, 3/2. The splitting between them is very small, 0.0148 eV * ½ kT, and it
can be neglected in many cases, i.e., consider the ground state as degenerate.
However, this cannot be done a priori, considering vibrational relaxation within the
NO ground state. Here we must take into account that in fact, we deal with two
states NO − X
2 P 1/2 and X
2 P 3/2 , whose E values differ by 0.0148 eV, and two
PECs correlated in the zero approximation to the of N(
4 S) + O(
3 P) limit. In the
zeroth approximation since there is a fine structure of the term O(
3 P J ), J = 2, 1, 0,
splitting DE 2-0 % 0.03 eV (see [8] and references). If we take this effect into
account, the picture will be even more complicated, so let us stop for now.
5.3 Vibrational Energy Transfer
165