LINE STRENGTH OF THE ATOMIC CHLORINE $^{2}P_{1/2}\leftarrow\ ^{2}P_{3/2}$ SPIN ORBIT TRANSITION

$^{1}$A. C. Stanton and C. E. Kolb, J. Chem. Phys. 72, 6637 (1980). $^{2}$A. C. Stanton, J.C. Wormhoudt, and J.W. Duff, in Spectral Line Shapes, Vol. 2, Walter de Gruyter, New York, 1983, p. 515. $^{3}$D.L. Flamm and V. M. Donnelly, Plasma Chemistry and Plasma Processing 1, 317 (1981).Author Institution: Aerodyne Research, Inc.; Aerodyne Research, Inc.Direct absorption or emission measurements of the ground state spin-orbit transitions in the halogen atoms ($^{2}P_{1/2}\leftrightarrow\ ^{2}P{3/2}$ magnetic dipole transitions) have been reported for iodine, bromine, chlorine, and $fluorine.^{1,2}$ In the case of atomic fluorine, tunable diode laser absorption measurements have established an accurate value for the radiative lifetime, in good agreement with a calculation. As noted in Ref. 1, the only other measurement of this forbidden transition in a halogen has been for iodine, where there is also reasonable agreement with calculations. We present the measurement by diode laser absorption of the radiative lifetime for the analogous transition in atomic chlorine, together with a comparison with theoretical calculations. Since chlorine atoms are the principal active species in plasma etching of semiconductors and metals using chlorine-containing $gases,^{3}$ diode laser absorption has the potential of being a very useful diagnostic of these important microelectronics fabrication processes