Determination of Ar-2(+) and N-4(+) recombination coefficients by subpicosecond multiphoton ionization at 248 nm and microwave interferometry

作者：Keister K E^*; Wagner C J; Putney J L; Hewitt J D; Eden J G

来源：Physical Review A, 2014, 89(1): 013401.

DOI：10.1103/PhysRevA.89.013401

Rate coefficients (alpha(D)) for the dissociative recombination of Ar-2(+) and N-4(+) in low-temperature plasmas have been determined by multiphoton ionization of the parent gas (Ar or N-2) at 248 nm, in combination with microwave interferometry at 9.2 GHz. A subpicosecond, Ti:Al2O3-KrF hybrid laser system generating 40 mJ pulses at 248 nm serves as a photoionization source within one arm of an interferometer having a bandwidth of similar to 800 MHz, thereby providing an ultrafast (delta-function) plasma channel generator and a noninvasive, microwave probe of the plasma that together decouple the ionization mechanism (and source) from the electron detection process. Comparisons of measurements of the temporally resolved electron density with numerical simulations find alpha(D) to be (1.2-6.0) x 10(-6) cm(3) s(-1) for Ar-2(+) and (2 +/- 1) x 10(-6) cm(3) s(-1) for N-4(+) for background pressures in the 150-600 Torr Ar and 10-400 Torr N-2 intervals, respectively. Both sets of constants are consistent with values reported previously in other ranges of gas pressure. The data and simulations indicate the cross section for four-photon ionization of Ar at 248 nm to be (5 +/- 3) x 10(-118) cm(8) s(3), or approximately 1.4 orders of magnitude lower than the single value in the literature [Uiterwaal et al., Phys. Rev. A 57, 392 (1998)]. Sub-50-ns transients observed in the electron density temporal profile for N-2 pressures above similar to 100 Torr suggest that the rate constant for N-2(B)-N-2(B) associative ionization is almost an order of magnitude larger than the currently accepted value.

• 出版日期2014-1-3