**5.1. The molecule predissociation in a void**

The predissociation of molecules is a non-radiant transition of the excited molecule with a stable electronic state to an unstable one with the same energy, accompanied by the dissocia‐ tion of the molecule [62]. The phenomenon of the molecule predissociation is explained on the basis of curves of potential energy. They are presented in Fig. 7a.

Under interaction with a photon, the molecule moves from the basic electron state (curve in Fig. 7a) into the excited one (curve 2); here the vibrational motion of the molecule enables the non-radiant transition to the repulsion curve (curve 3), which leads to the dissociation of the molecule. Being in the predissociation state, the molecule dissociates if its full energy exceeds the energy of separated particles that diverge along the potential curve of repulsion. Particles scatter with a kinetic energy

$$
\varepsilon\_{\text{kin}} = \varepsilon\_{\text{pr}} - \mathbf{D}\_0 \tag{15}
$$

where εpr is the predissociation energy and D0 is the energy of molecule dissociation. In the case of a gently sloping repulsion curve, D<sup>0</sup> can have a smaller departure from εpr. If there is no separation then from Eq. (15) it follows that

$$
\boldsymbol{\varepsilon}\_{\rm pr} = \mathbf{D}\_{0\prime} \tag{16}
$$

because in this case εkin=0. Therefore, the energy of molecule predissociation, εpr is a limit for the energy of dissociation, D0.

**Figure 7.** (a)-predissociation scheme under molecule transition to the repulsion curve: 1 and 2 are attraction curves in the basic electronic state and in the excited electronic state, respectively; 3 is the repulsion curve; εn and D0 are energies of predissociation and dissociation, respectively; D is the kinetic energy of the scattered atoms [62]. (b)-Predissociation in the scheme of energy states in the cell of a periclase crystal after the resonance absorption of a photon with energy ZΔ*H*subl/*N*A. The particles are in the sites of the crystal lattice (states 1 and 2); in state 3 the particles are displaced in the nanovoids of the crystalline structure of the crystal as a solid system.

### **5.2. The photopredissociation in a void of an ideal crystal**

**4.3. The atom and nanovoid as two entities of an antenna processin a crystal**

**5. The nanovoid and predissociation of an ideal crystal cell**

elemental cell of the crystal serves as an example of such a fragment.

basis of curves of potential energy. They are presented in Fig. 7a.

**5.1. The molecule predissociation in a void**

no separation then from Eq. (15) it follows that

scatter with a kinetic energy

the energy of dissociation, D0.

the photon, it may be considered an antenna process.

130 Solar Cells - New Approaches and Reviews

Thus, the action of the photon antenna in the crystal may be considered a reversible movement of the particle from its equilibrium position (for example, the lattice's site) into a nanovoid, and this nanovoid is forbidden from being steadily filled in by the symmetry of placement of the neighbor particles. This nanovoid pushes out the particle resulting in photon absorption in the initial position. If this cycled process is accompanied by the absorption and radiation of

The sublimation, dissociation, or destruction of a crystal is the process of destroying those chemical bonds that place atomic particles in the space periodically. This section examines the crystal predissociation as a state of its particles that follows after the breaking of the chemical bonds of the crystal cell and directly precedes their scattering. A description of the crystal predissociation is missing in the literature, but it is similar to the predissociation of molecules in gas, which has been studied well enough. In this section, we consider the fragments of an ideal crystal. These fragments are restricted based on the number of atomic particles. The

The predissociation of molecules is a non-radiant transition of the excited molecule with a stable electronic state to an unstable one with the same energy, accompanied by the dissocia‐ tion of the molecule [62]. The phenomenon of the molecule predissociation is explained on the

Under interaction with a photon, the molecule moves from the basic electron state (curve in Fig. 7a) into the excited one (curve 2); here the vibrational motion of the molecule enables the non-radiant transition to the repulsion curve (curve 3), which leads to the dissociation of the molecule. Being in the predissociation state, the molecule dissociates if its full energy exceeds the energy of separated particles that diverge along the potential curve of repulsion. Particles

where εpr is the predissociation energy and D0 is the energy of molecule dissociation. In the case of a gently sloping repulsion curve, D<sup>0</sup> can have a smaller departure from εpr. If there is

because in this case εkin=0. Therefore, the energy of molecule predissociation, εpr is a limit for

kin pr 0 ε =ε - D (15)

pr 0 ε = D , (16)

According to the Frank-Kondon principle, the transition corresponding to the crossing attraction and repulsion curves is the most probable. From (Fig. 7a) one can suppose that Eq. (17):

$$
\mathfrak{E}\_{\text{pr}} \triangleq \mathfrak{E} \tag{17}
$$

is correct, where ε is the energy of the absorbed photon. Joining Eq. (16) and (17) we obtain

$$
\varepsilon\_{\rm pr} = \mathbf{D}\_0 = \varepsilon \tag{18}
$$

There are no molecules in ionic and covalent crystals, or in amorphous and liquid solids. However, we can write equations similar to Eq. (16)– (18) for the condensate state of the matter.

In laser technology, the film's solid target is under the action of a powerful radiation flux. If this power is over 109 W/m2 , the sublimation of the target occurs. The expression for the kinetic energy of the i-particles can be written by analogy with Eq. (15) in this form:

$$
\varepsilon\_{\text{kin}} = \varepsilon\_{\text{pr}} \cdot \text{f} \langle \mathbf{D}\_{\text{sub} \mathbb{M}} \cdot \mathbf{Z} \rangle\_{\text{\textdegree \cdot}}
$$

where εpr is the energy of cell predissociation consisting of *Z* chemical formula units, giving birth to i-particles, and Dsubl is the energy of sublimation of a mole of chemical formula units. When the laser radiation power is less than 109 W/m2 , a crystal melts. At still lower radiation capacities, for example, in the spectral experiment, the destruction of the crystal does not take place, i.e. the value εkin=0. Assume also that

$$\varepsilon = \text{f(D}\_{\text{subb}} \text{ } \text{Z} \text{'} \varepsilon\_{\text{pr}}) .$$

describes the interaction of radiation with the solid in regards to which predissociation states may be realized.

As an example, we consider the cell of periclase (Mg4O4), while *Z*=4. The cell can increase its potential energy through the resonance absorption of a photon with energy ε. Then, according to Fig. 7 we can write

$$\left(\mathrm{Mg}\_4\mathrm{O}\_4\right)^0 = \left(\mathrm{Mg}\_4\mathrm{O}\_4\right)^\* + \varepsilon,\tag{19}$$

where (Mg4O4) 0 is the basic state of the cell and (Mg4O4)\* is an excited state. We can write

$$\mathrm{Mg}\_4\mathrm{O}\_4\mathrm{(crystal)} = 4 \,\mathrm{MgO} \,\mathrm{(quasi-gas)} + \mathrm{Z\Lambda H}\_{\mathrm{salt}} / \mathrm{N}\_{\Lambda'} \tag{20}$$

Comparing Eq. (19) and (20) one can acknowledge that if the states

 $(\mathrm{Mg}\_4\mathrm{O}\_4)^0$ and  $\mathrm{Mg}\_4\mathrm{O}\_4$ (crystal)

are energetically identical, the predissociation of the crystal cell in Fig. 7 may be presented as a transition

$$(\mathrm{Mg\_4O\_4})^\* \rightharpoonup 4 \text{ MgO (quasi-gas)}$$

between energetically identical states if ε=ZΔ*H*subl/*N*A.

Shown below are the particles filling the crystallographic cells; this process is accompanied by the formation of nanovoids in the space of an ideal crystal. Filling in these nanovoids can damage the cells' symmetry. If the particles can temporarily move into these nanovoids after photon absorption, we have a prerequisite for the particles' predissociation as a stage of the antenna process without any damage to the symmetry of the crystal as a whole.
