Decay of Metastable Helium Molecules (^3∑u^+) and Atoms (^3S) in an Afterglow*

Experimental evidence from pulsed afterglow studies is presented which demonstrates that thermal energy charge transfer is the primary source of excitation for the high-lying Zn II and Cd II laser levels, with configurations of the type 3d IOnx and 4d IOnx, respectively, whereas the main source of excitation of the Zn II and Cd II laser levels, with configurations of the type 3d 94s 2 and 4d 95s 2, is Penning ionization. The total velocity-averaged cross sections for thermal energy charge exchange and for Penning ionization are measured to be of order 10-15 em'. These large cross sections account for the relatively high efficiency and low threshold currents characteristic of He-Zn and He-Cd ion lasers. The intensity of spontaneous emission from laser levels excited in a flowing afterglow by charge-transfer reactions is broken down into the component contributions: direct charge-transfer excitation, radiative cascade, and collisional cascade excitation. The results are used to estimate the values of the individual cross sections for direct charge transfer into Zn II and Cd II laser levels. The potential of thermal energy charge transfer as a general excitation scheme for gaseous lasers is illustrated by several new proposals for new cw laser transitions in the region between 2000 and 4000 Ji.:

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Fine structure of the metastable a3Σu+ state of the helium molecule

Lichten

McCusker

Vierima

1974

The Journal of Chemical Physics

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Lifetimes of fine structure levels of metastable H2 in the c 3Π u state J. Chem. Phys. 70, 4376 (1979); 10.1063/1.438010 Fine structure of the metastable a 3Σ u + state of the helium molecule. Further results J. Chem. Phys. 69, 98 (1978); 10.1063/1.436350 Some Excited States of the Helium Molecule. I. The Lowest 1Σ u + and 3Σ g + States and the First Excited 1Σ g + StatesWe have measured the spin-spin, electronic fine structure of the a 3~~ metastable state of He, by means of a molecular beam, magnetic resonance apparatus, with the flowing afterglow of a pulsed, helium discharge as the source. The zero field separations in the N = I and N = 3 rotational levels, probably in the v=O vibrational state, are (in MHz) N=I: J=0#J=1:2199.968 ±0.01, J = I #J = 2: 873.668 ±0.007; N= 3: J= 2#J~ 3: 1323.911±0.006, J=3#J=4: 964.992±0.006, where the errors quoted· are three standard deviations of the mean. From these measurements and from a separate determination of the level order, the interaction constants for these states are the following (in MHz): spin-spin: A.:-\098.773 ±0.OO5(N = I), -1096.803±0.004(N =3), spin-rotation: r: -2.421±0.OO3(N = I), -2.414±0.OOI(N =3), where the errors are 3u. Spin-spin interactions in moleculesMolecules in 3Z; states are of interest, because the first order fs is caused by magnetic, spin-spin interac-

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Decay of Metastable Helium Molecules (^3∑u^+) and Atoms (^3S) in an Afterglow*

Cited by 5 publications

References 7 publications

Time resolved studies of rare-gas molecular emission in the vacuum ultraviolet: Helium and argon

Time resolved studies of rare-gas molecular emission in the vacuum ultraviolet: Helium and argon

Excitation mechanisms in He–Cd and He–Zn ion lasers

Fine structure of the metastable a3Σu+ state of the helium molecule

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