The cross section for the excitation of the (0, 0) first negative band of N2 by electron impact has been measured, using photon-counting techniques, in the energy range from threshold to 3 keV and extrapolated to 10 keV by means of a Bethe-Oppenheimer relation. In order to avoid polarization effects, the primary measurements were made at the "magic angle" of 54' 44'; complementary measurements at 90' were also obtained for comparison purposes. The excitation cross section for the (0, 0) band reached its maximum value at an energy of about 100 eV where it was (1.74 +0.17) && 10 cm . The ratio of the total ionization cross section to the excitation cross section was nearly constant over the energy range from 30 eV to 10 keV, and had a value of 14.1.

The excitation of argon and helium metastables by electron impact was studied in the energy range from threshold to about 50 eV with a time-of-flight method. The metastables were detected by Auger ejection of secondary electrons from a CuBeQ surface. The argon cross section was obtained in two different ways yielding peak cross sections of 3.4 X10 and 3.7 & 10~7 cm2 at 22 eV, respectively. The estimated uncertainty for both values is a factor of 2. The helium cross section was measured with a trapped-election method near threshold and found to have a peak value of (6.2+ 2.0)x 10 8 cm at the 2g-eV maximum. The secondaryelectron yields of the metastable detector used in this work are discussed in detail. The effect of metastable recoil is also discussed. Argon metastables suffer only negligible recoil because of their large atomic weight, but this is not the case for the lighter helium metastables.

The average lifetime of metastable CO molecules in the a II state excited by electron impact at 7. 5 eV at room temperature was found to be about 1 msec. Lifetimes of metastable N2 molecules in the a'0~and E Z~s tates were found to be 115+20 and 190 +30 @sec, respectively. There was evidence for at least one higher-lying metastable state of CO at about 10eV having a lifetime of about 0. 1 msec. The lifetimes were obtained in a time-of-flight experiment and deduced from the measurements without resorting to analytic expressions of the time-of-flight distribution.The observed time-of-Qight distributions were essentially Maxwellian. A diffuse-gas source operated at pressures in the 10 4-Torr range was used. Effects due to metastable recoil, uv photons from metastable decay, and metastable wall collisions were carefully examined and found to be negligible under most conditions. Metastable excitation functions were obtained using a low-energy high-resolution electron gun.

Vacuum ultraviolet multiplets of Cr, Cn, and Or have been produced by electron impact on CO 2 . Absolute emission cross sections for these multiplets have been measured from threshold to 350 eV. The electrostatically focussed electron gun used in this series of experiments is described in detail. The atomic multiplets which were produced by dissociative excitation of CO2 and the cross sections at 100 eV are: Or (2p' 3p_ 2p 3 3s 3S) 1304 A-1.04X10--18 cm 2 ±18%; Cr(2s 2 2p2 3P-2s2p3 3PO) 1329 A-2.67XlO-19 cm 2 ±21%; Cr(2s 2 2p23P-2s2p33JYl) 1561 A-7.50X 10--19 cm 2 ±30%; Cr(2p23P-2p3s 3 po) 1657 A-1.45 X 10-18 cm 2 ±23%; Cn(2s 2 2p 2po-2s2p2 2D) 1335 A-7.60X 10-19 cm 2 ±22%; and Cn (2s2p2 2D-2p3 2JYl) 1324 A-1.33X 10-20 cm2±23%. The dependence of the excitation functions on electron energy shows that these mUltiplets are produced by electric-dipole-allowed transitions in CO2•