Spin-Dependent Processes in Gases
and Gas Discharge Plasma



Inter-atomic and atomic-molecular spin-dependent interactions

The method of optical orientation of atoms is successfully applied in laboratory to studying of interaction of atoms at their collisions. In particular, researches on studying of transfer of polarisation from the optially oriented atoms to other atoms as a result of their interaction in the course of various collision processes such as a spin exchange, an exchange of metastability, hemoionization, etc. The other collision processes leading to a relaxation of spin atom polarisation, for example such as diffusion, spin-randomization, and also shifts of frequency of a magnetic resonance, etc, are also studied. The most interesting researches in the field of atom-molecular collisions which are or were carried out are listed below:

  • Using optical orientation method, elastic and non-elastic collisions between polarized atomic particles were investigated, as well as spin-dependent inter-atomic, electron-atomic, atomic-molecular interactions in gas and gas discharge plasma.

  • Using both resonant and non-resonant radiospectroscopy methods, diffusion coefficients of alkaline atoms, hydrogen, deiterium in various buffer gases were measured.

  • R.A.Zhitnikov and B.N.Sevastjanov have discovered the influence of the optical orientation of He atoms upon plasma conductivity, caused by spin dependence of the probability of Penning ionization. Later spin-dependent Penning collisions between metastable Helium atoms and alkaline atoms were investigated, as well as their influence upon gas discharge plasma conductivity.

  • A new method of spin polarization of the hydrogen isotopes is suggested and developed experimentally.

  • The kinetics and the dynamics of the spin-exchange H+H collisions in the temperature range 0.01-1000oK has been investigated.




Elastic and Inelastic Processes
with Spin-Polarized Metastable Helium Atoms In Gas Discharge



At the interaction between the spin-polarized excited atom and paramagnetic ground state atom or molecule in gas discharge, elastic and inelastic processes take place simultaneously. It means that besides the chemo-ionization of the atom or molecule at the expense of atom's excitation energy (inelastic process), an exchange of electrons is possible without a great depolarization (elastic process, or spin exchange). In such a case these two processes give rise to a remarkable spin polarization transfer between colliding particles. Influencing on each other, these two processes result in change of the spin exchange and frequency shift cross section values.

The helium metastable atoms (He*), having a large store of internal energy (19.8 eV), are capable of ionizing the molecule or atom (B) even at the thermal energies of relative motion


He* + B → (HeB)* → ionization products        (1)


Usually investigations are performed with unpolarized particles, and the cross sections for decay of metastable's states due to collisions with molecules and atoms are determined. Experiments with polarized particles give one a possibility to obtain information about elastic processes. Due to the paramagnetism of the partner of the collision (the ground state alkali atoms, paramagnetic molecules, and hydrogen atoms) the spin-exchange process


He*(m1) + B(m2) → (HeB)* → He*(m'1) + B(m'2),        (2)


is possible simultaneously with chemo-ionization (1), where m1 and m2 are the projections of the magnetic moments of the atomic particles.

The kinetic equations, describing such a situation in the optical pumping experiment, were obtained. The expression for the spin-exchange and frequency resonance shifts cross sections of processes, taking into account the mutual influence, were derived. It was shown that the complex elastic cross sections do significantly change because of the chemo-ionization process. It gave us a possibility to get information about spin-exchange and chemo-ionization cross sections from the optical orientation and magnetic resonance experiments. In the frame of complex interaction potentials energy dependences of the chemo-ionization, spin-exchange and frequency shift cross section were obtained for the systems ⌠polarized helium metastable atoms - ground state alkali atoms, or paramagnetic molecules, or hydrogen atoms■.
Contacts:
Kartoshkin V.A.
Klementiev G.V.



PUBLICATIONS
  1. Dmitriev,SP; Dovator,NA; Zhitnikov,RA; Kartoshkin,VA; Melnikov,VD. Observation of a circular dichroism of an ensemble of triplet metastable helium atoms in a Na-He gas-discharge plasma with laser-oriented sodium atoms. 2000, Tech. Phys., v.45, 1, pp.14-16

  2. Dmitriev,SP. Effect of the optical orientation of spin angular momenta of sodium atoms in the 3(2)S(1/2) state and metastable helium atoms in the 2(3)S(1) state on the Na-He gas-discharge plasma conduction. 2000, Opt. Spectrosc., v.88, 5, pp.664-666

  3. Dmitriev,SP; Dovator,NA; Zhitnikov,RA; Kartoshkin,VA. A change in the conductivity of sodium-helium plasma interacting with polarization-modulated laser radiation tuned to sodium D-1 line. 2001, Jetp Lett., v.73, 11, pp. 597-599

  4. Dmitriev,SP; Dovator,NA; Zhitnikov,RA; Kartoshkin,VA. Polarization optogalvanic effect in sodium-helium plasma. 2001, Tech. Phys., v.46, 6, pp.700-703

  5. Dmitriev,SP; Dovator,NA; Kartoshkin,VA. Measurement of the spin-exchange and chemical ionization rate constants in collisions of polarized metastable 2(3)S(1) helium atoms with 3(2)S(1/2) sodium atoms. 2009, Tech. Phys., v.54, 10, pp.1557-1559

  6. Dmitriev,SP; Dovator,NA; Kartoshkin,VA. Spin exchange rate constant for collisions of metastable helium atoms with rubidium atoms.2008, Tech. Phys. Lett., v.34, 8, pp.693-695.

  7. A.I.Okunevich, Spin-Exchange with Account for acting of the Hyperfine Interaction of Electron and Nuclear Spins during the Collision, Opt. Spectr., V. 77, p.160 (1994); V. 79, p. 8 (1995)