Time-resolved measurements of ionization and vibration-to-electronic energy transfer in optically pumped plasmas

A method for direct measurements of electron number density, ionization rate, and the electron–ion recombination rate coefficient in optically pumped non-equilibrium plasmas has been developed. In this method, a pulsed, non-self-sustained discharge created by applying square-shaped, below breakdown voltage pulses to two electrodes placed outside the plasma (a Thomson probe) is used to remove electrons from the plasma. The electron number density is inferred for CO/Ar and CO/N2 optical mixtures with small amounts of O2 additive present. The results are compared with microwave attenuation measurements. The electron–ion recombination rate coefficients in CO/Ar/O2 and in CO/N2/O2 plasmas are β = (3–4) × 10−8 cm3 s−1 and β = (2–3) × 10−7 cm3 s−1, respectively. Time-dependent measurements of the electron concentration and vacuum ultraviolet radiation (CO fourth positive system) are used to study the mechanism of CO(A1Π) population in the optically pumped plasma. The experimental results are compared with kinetic modelling calculations. The results systematically show that the intensity of the CO fourth positive radiation closely follows the electron number density in the laser-excited plasma region after the Thomson probe voltage is turned on or off. This demonstrates that electrons play a major role in the excitation of the A1Π electronic state of CO and provides additional evidence that vibrational-to-electronic (V–E) energy transfer in plasmas sustained without external electric fields is mediated by collisions with electrons.

[1]  W. Lempert,et al.  MITIGATION OF OXYGEN ATTACHMENT IN HIGH PRESSURE AIR PLASMAS BY VIBRATIONAL EXCITATION , 2004 .

[2]  I. Adamovich,et al.  CHARACTERIZATION OF ELECTRON-MEDIATED VIBRATION- ELECTRONIC (V-E) ENERGY TRANSFER IN OPTICALLY PUMPED PLASMAS USING LANGMUIR PROBE MEASUREMENTS , 2002 .

[3]  I. Adamovich,et al.  Mitigation of Electron Attachment and Recombination in Atmospheric Pressure Air Plasmas , 2002 .

[4]  I. Adamovich,et al.  Electron-mediated vibration–electronic (V–E) energy transfer in optically pumped plasmas , 2001 .

[5]  I. Adamovich,et al.  Electron density and recombination rate measurements in CO-seeded optically pumped plasmas , 2001 .

[6]  Igor V. Adamovich,et al.  Control of electron recombination rate and electron density in optically-pumped non-equilibrium plasmas , 2001 .

[7]  I. Adamovich,et al.  Ionization measurements in optically pumped discharges , 2000 .

[8]  I. Adamovich,et al.  Time-resolved Fourier transform infrared spectroscopy of optically pumped carbon monoxide , 2000 .

[9]  Igor V. Adamovich,et al.  The effect of superelastic electron-molecule collisions on the vibrational energy distribution function , 1996 .

[10]  I. Adamovich,et al.  Vibrationally stimulated ionization of carbon monoxide in optical pumping experiments , 1993 .

[11]  R. Johnsen.  Recombination of cluster ions , 1993 .

[12]  Robert L. DeLeon,et al.  Vibrational energy exchange rates in carbon monoxide , 1986 .

[13]  J. Rich,et al.  4 – Relaxation of Molecules Exchanging Vibrational Energy , 1982 .

[14]  Richard F. Sincovec,et al.  General Software for Two-Dimensional Nonlinear Partial Differential Equations , 1981, TOMS.

[15]  R. F. Sincovec,et al.  Algorithm 565: PDETWO/PSETM/GEARB: Solution of Systems of Two-Dimensional Nonlinear Partial Differential Equations [D3] , 1981, TOMS.

[16]  Y. Kaufman,et al.  Ion clusters in He–Co and Ar–Co glow discharges , 1980 .

[17]  K. Budden.  The diffusion and drift of electrons in gases: L. G. H. Huxley and R. W. Crompton. Wiley, New York, XXV + 669 pp. Price £19.60 , 1976 .

[18]  R. G. Rehm,et al.  Vibrational Relaxation of Anharmonic Oscillators with Exchange‐Dominated Collisions , 1968 .

[19]  H. Taylor,et al.  Resonance Scattering of Slow Electrons from H 2 and CO Angular Distributions , 1968 .

[20]  E. W. McDaniel,et al.  Collision phenomena in ionized gases , 1964 .