Dissociation of Benzene Molecule
in a Strong Laser Field
The number of articles devoted to the interaction of molecules with a
strong laser field increased considerably in recent years. The main
features of interaction between diatomic molecules and a laser radiation
were considered in a great number of experimental [1-5] and theoretical
[6-9] papers. Classical and quantum investigations of spatial alignment
of diatomic molecules and their molecular ions in a strong laser field,
as well as ionization and dissociation of these molecules and their
molecular ions account for physical pictures of all processes.
However, when considering complex organic molecules, we observe physical
phenomena to be richer, and they are not thoroughly investigated. Most
of results obtained for diatomic molecules can be generalized to the
multi-atomic molecules. This short paper contains the results of
theoretical derivations for dissociation of benzene molecule C6H6 in the
field of linearly polarized Ti:Sapphire laser. Data were taken from
experimental results by Chin’s group, Ref. . We use the atomic system
of units throughout the paper.
2. Theoretical approach.
Let us consider the benzene molecule C6H6 in the field of Ti:Sapphire
laser with the wavelength =400 nm, pulse length =300 fs and maximum
intensity Imax=21014 W/cm2. According to Ref.  first electron is
ejected from this neutral molecule and then the dissociation of
The most probable channel for decay of this ion is the separation into
the equal parts :
Of course, there is another channel for decay of C6H6+-ion which
includes the ejection of the second electron and subsequent Coulomb
explosion of the C6H6++-ion. We do not consider the latter process.
The channel (1) is seen to be similar to the dissociation of the
hydrogen molecular ion considered in Ref. . Indeed, the model scheme
of energy levels for C6H6+-ion (see Ref. ) reminds the model scheme
of energy levels for H2+  containing only two low-lying electronic
levels: 1g (even) and 1u (odd).
Therefore we consider the dissociation process of C6H6+-ion
analogously to that for H2+-ion (see Fig. 1). The benzene molecular ion
has the large reduced mass with respect to division into equal parts.
Hence, its wave function is well localized in space (see Fig. 2) and
therefore we can apply classical mechanics for description of the
dissociation process (1). However, the solution of Newton equation with
the effective potential (see below) does not produce any dissociation,
since laser pulse length is too small for such large inertial system. In
addition to, effective potential barrier exists during the whole laser
pulse and tunneling of the molecular fragment is impossible due to its
large mass ( see Fig. 2). Thus, we should solve the dissociation problem
in the frames of quantum mechanics.
The ground even electronic term of C6H6+-ion is presented here in the
form of the well-known Morse potential with parameters =2k and De=6.2
0