Навигация
3. Results.
The quantity W(t) is seen from Fig. 4 increase exponentially with time and it is equal to 0.11 after the end of laser pulse. It should be noted that the dissociation process can not be considered as a tunneling of a fragment through the effective potential barrier (see Fi. 2). Indeed, the 
tunneling probability is on the order of magnitude of
Where Veff is substituted for maximum value of the field strength and the integral is derived over the classically forbidden region under the effective potential barrier. The tunneling effect is seen to be negligibly small due to large reduced mass of the molecular fragment m>>1. The Keldysh parameter g=w(2mE)1/2/F>>1. Thus, the dissociation is the pure multiphoton process. The frequency of laser field is w µ 2.7 эВ, while the dissociation potential is De=6 eV. Hence, three-photon process of dissociation takes place. The dissociation rate of three-photon process is proportional to m-1/2. The total dissociation probability is obtained by means of multiplying of this rate by the pulse length t. Therefore the probability of three-photon process can be large, unlike the tunneling probability. This is the explanation of large dissociation probability W»0.11 obtained in the calculations.
4. Conclusions.
Derivations given above of dissociation of benzene molecule show that approximately 11% of all C3H3+-ions decay on fragments C3H3 and C3H3+ under the conditions of Ref. [4]. The absorption of three photons occurs in this process.
Author is grateful to N. B. Delone, V. P. Krainov, M. V. Fedorov and S. P. Goreslavsky for stimulating discussions of this problem. This work was supported by Russian Foundation Investigations (grant N 96-02-18299).
References
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4. A. Talebpour, S. Larochelle and S. L. Chin, in press.
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9. M. E. Sukharev, V. P. Krainov, JETP, 83, 457,1996. M. E. Sukharev, V. P. Krainov, Laser Physics, 7, No3, 803, 1997. M. E. Sukharev, V. P. Krainov, JETP, 113, No2, 573, 1998. M. E. Sukharev, V. P. Krainov, JOSA B, in press.
Figure captions
Fig. 1. Scheme of dissociation for benzene molecular ion C6H6+.
Fig. 2. The Morse potential (a), the effective potential (b) for maximum value of the field strength (a.u.), and the square of the wave function of the ground state for benzene molecular ion (c) as functions of the nuclear separation R (a.u.) between the fragments C3H3 and C3H3+.
Fig. 3. Envelope of laser pulse as a function of time (fs).
Fig. 4. The dissociation probability of benzene molecular ion C6H6+ as a function of time (fs).
 |  |
Fig. 1
Morse potential (a) (a.u.),
effective potential for max. field (b) (a.u),
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|
|
 |
square of the wave function of the ground state for benzene molecular ion (c)
R, a.u.
Fig. 2
t, fs
Fig. 3
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W(t)
t, fs
Fig. 4
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