Mobilities, Diffusion Coefficients, and Reaction Rates of Mass-Indentified Nitrogen Ions in Nitrogen

Abstract

Measurements at room temperature of the drift velocity, the longitudinal diffusion coefficient, and the transverse diffusion coefficient have been made for low-energy mass-identified nitrogen ions in nitrogen gas in a drift-tube mass spectrometer. These parameters were evaluated using an analysis described in the article immediately preceding this one. The mobilities of N+ and N2+ were obtained over the E/N range from 7 to 700 x 10 V cm, yielding zero-field reduced mobility values of 2.97 and 1.87 cm /V sec, respectively. The mobilities of N3+ and N4 were obtained over the E/N range from 2 to 40 x 10 V cm, yielding zero-field reduced mobility values of 2.26 and 2.33 cm /V sec, respectively. For N+ and N2+, the longitudinal diffusion coefficients were determined from the widths of the expeximental arrival time spectra, and the transvexse diffusion coefficients were determined from the attenuation of the ion count rate as the drift distance was increased. For both ions the two diffusion coefficients were observed to be equal and in agreement with the Einstein relation at low E/N, but to behave quite differently as E/N was increased. It has previously been reported that the longitudinal diffusion coefficients of both ions increase rapidly by more than an order of magnitude; the transverse diffusion coefficient of N+ has been found to increase in a similar fashion, although much less rapidly, while that of N~+ remains nearly constant, Measuxements were made up to an E/N of 700 & 10 V cm . The rates of the two ion-molecule reactions, N++2N~N3++N2 and N2 +2N& N4 +N2, were also measured by an attenuation technique over the E/N range from thermal to 100 x 10 V cm . The reaction rates at thermal energy were determined to be 1.8 && 10 cm /sec and 5.0 x 10 cm /sec, respectively, and both rates were observed to decrease as E/twas increased. I. INIODUCTIONThis article presents the results of an extensive investigation of the drift, diffusion, and reaction of lom-energy nitrogen ions in nitrogen gas at room temperature.The data mere obtained with a drift-tube mass spectrometer of ultra-highvacuum construction. Using an analysis discussed in the preceding paper, ' the mobilities of N+, N, +, N, , and N~i ons in nitrogen gas have been determined, both the longitudinal (Dl ) and the transverse (DZ ) diffusion coefficients of N and N, + have been measured, ' and the reaction-rate coefficients for the three-body ion-molecule reactions have been evaluated.The mobility K is defined' as the ratio of the drift velocity e~t o the electric field strength E, and is inversely proportional to the gas numbex density ¹ To facilitate comparisons of data obtained at different gas number densities, we shall make use of the "reduced mobility" II"» defined by the equation where p and 7. " are the gas pressure and temperature, in Torr and deg Kelvin, respectively, at which the measurement of K was made. At a given temperature T, the parameter E/N determines the average energy and the transport properties of the ions. Hence the data are present...

Cation transport in gaseous nitrogen: density and temperature effects

“…for N2+ and N4+ at 220 + 20 K (7). The mobility of N3+ has only been measured at 300 K , where it is essentially the same as that of N4+ (6).…”

“…The N4+-N2 momentum transfer cross section as a function of collision energy E was extracted from the (np., T ) values by numerically fitting them to eq. [6] (12).…”

Experimental Study of Shock Wave Dynamics in Magnetized Plasmas

“…8 The definition of the reduced ion mobility μ oi is given in Ref. 14 is the discharge gas temperature in K (assuming T i ≈ T g ). At fixed operating pressure p = 15 Torr and calculated discharge gas temperature T g = 349.6 K, the mobility of the argon ions is estimated to be μ i = 108.35 cm 2 V -1 s -1 .…”

Mathematical analysis of reactive ion transport in dynamic equilibrium: The case of two ionic species

“…udl = 2.5 X lo4 cm s-l, ud2 = 2 X lo4 cm s-I, DZl = D,, = 125 cm2 s-I, DZ2 = Dr2 = 100 cm2 S-I, a2, = lo's-', a12 = 2 X lo4 s-'. Two solid-line curves are exact arrival time spectra generated from [4]- [6] by using a numerical quadrature. The two broken-line curves are approximate ATS calculated from [18].…”

“…T I and T 2 are expressed as where DZi and Dri are longitudinal and transverse diffusion coefficients of ith species, respectively. By applying the expansion technique in [5] and [6], we can derive an explicit form of the solutions as follows:…”