MOTION OF GASEOUS IONS IN STRONG ELECTRIC FIELDS 179 



a, a = — = ionic acceleration. 

 m 



b = impact parameter. 



6iini = limiting value of the impact parameter separating hyperbolic 



and spiralling orbits (equation (125)). 

 c, c, c', Cz , Cf , Ci = various ionic velocities or components. 

 ex , ey , ez = energies of ionic motion (or "high field" parts thereof) 



along X, y, z. 

 Bz* = random part of the above energy, 

 it = total particle current density of the ions (may be a function of 



r and t). 

 j = partial current density induced by the concentration gradient; see 



equation (22). 

 k = Boltzmann's constant (only when followed directly by T). 

 /c, k = relative concentration gradient of the ions (a different use is 



made of k in Section HE). 

 n = number density of the ions (may be a function of r and t). 

 p, q, r, s = undetermined constants; used three times independently 



(equations (82), (90) and (160)). 

 p(0)^ p(i^ ^ various approximations to these numbers, 

 u, u', V = ionic velocities. 



w = ionic velocity rendered dimensionless (see eq. (75) or (85)). 

 ^ = the inner integral in the double integral eq. (69). 

 C, C = molecular velocities. 

 X) = ionic diffusion tensor. 

 D\\ , Dx = components of above tensor parallel and perpendicular to 



the field. 

 M = molecular mass. 

 N = number density of the molecules. 

 P = molecular polarizability. 

 T = gas temperature. 

 U, U' = molecular velocities. 

 X,Y = left and right hand sides of equation (Ilia). 



^ = — - = temperature parameter (A different use of ^ is made 



in Section IIIB where it is the relative impact parameter b/bum)- 

 Yj T^ V^ v' = relative velocities of ion and molecule. 

 ^, T}, ^ = cartesian coordinates oriented on c. 

 p = distance between ion and molecule, 

 o- = collision cross section of ions and molecules (may be a function of t)- 



