Role of metastable atoms and molecules of helium in excitation transfer tohydrogen atoms

The afterglow of a discharge in helium with a small admixture of hydrogen i s studied spectroscopically (p = 40 Torr, [e] less than or equal to 10(11) cm(-3)). The time-resolved measurements of intensities of the first four li nes of the Balmer series are performed. The concentrations of metastable he lium atoms and molecules are evaluated from the relative intensity of the a bsorption lines. The ratios of excitation transfer rates from atoms He(2 S- 3(1)) k(1)(n) and molecules of helium He-2(a 2s sigma 3 Sigma(u)(+)) k(2)(n ) to atomic hydrogen H*(n) are measured to be k(1)(n = 3)/k(2)(n = 3) = 0.0 4 +/- 0.02 and k(1)(n = 4)/k(2)(n = 4) = 0.01 +/- 0.02. The ratios of excit ation rate constants k(2)(n) corresponding to different states H(n) are mea sured to be k(1)(n = 4)/k(2)(n = 3) = 0.023 +/- 0.01; k(1)(n = 5)/k(2)(n = 3) less than or equal to 0.013; and k(1)(n = 6)/k(2)(n = 3) less than or eq ual to 0.007. (C) 2000 MAIK "Nauka/Interperiodica".