Tunnel ionization of diatomic atmospheric gases (N₂, O₂) by laser radiation

Abstract

We present the results of calculation of the rates of tunnel ionization of N 2 and O 2 molecules from the ground and excited vibrational states by linearly polarized laser radiation. These data are necessary for the theoretical description of filamentation. For N 2 , we consider ionization from the 3σ g and 1π u shells, which give comparable contributions. For O 2 , we consider ionization from both the ground X 3 Σ − g and excited a 1 ∆ g electronic terms. We demonstrate that for N 2 , the ionization rate is maximum when the electric field vector of laser radiation is directed along the molecular axis (for 3σ g shell) or perpendicular to it (for 1π u shell), whereas for the O 2 molecule, for both electronic states considered, the rates have maxima when the angle between the electric field and molecular axis is equal to 45°.

Modification of Vibrational Parameters of a CO2 Molecule by a Laser Field: Impact on Tunnel Ionization

“…In our papers [11,13,[25][26][27]34], a tunnel ionization theory is developed that accounts for internal degrees of freedom of the molecular target. The molecular core effects taken into account can be roughly divided into three groups:…”

“…This theory was further developed in refs. [25,26]. It was shown that this method can be used for laser isotope separation.…”

“…In refs. [11,25,26,34], the ITE model was expanded onto the molecules by the account for the vibrational degrees of freedom. In our theory, this is reflected in the change of the term ∆ and modification of the Dyson orbital by the vibrational multiplier (see (8)).…”

“…Here, N HOMO is the number of equivalent electrons in HOMO (the tunnel ionization from deeper shells of HOMO-1, HOMO-2, etc., are generally suppressed due to higher ionization energy-see also discussion in Section 3.2); the second, third and fourth multipliers are given by Equations ( 3), ( 10) and (26), respectively; the square of the vibrational overlap integral is called the Franck-Condon factor (FCF); µ i, f is the quantum numbers defining the electronic states of the neutral molecule or its ion:…”

“…Note that the anti-Stokes enhancement was not taken into account by other authors [15][16][17][18][19][20][21][22][23][24]. This effect can be potentially used for the laser separation of hydrogen [11], nitrogen and oxygen [25,26] isotopes in gas targets. Due to the specific vibrational structure of CO and CO + , the carbon monoxide, CO, was shown to be useless for the laser separation of carbon isotopes [27].…”