Transition Probabilities of Forbidden Oxygen Lines in a Discharge Tube

Abstract

We have studied emission of the four forbidden lines of atomic oxygen, λλ 6364, 6300, 5577, and 2972 Å from a discharge through flowing tank oxygen at pressures of a few torricelli, in a tube of 8 mm i.d., with 40–120 mA of current flowing. We found that under these discharge conditions none of the lines were perceptibly broadened or shifted (to within 0.2 Å), and that none showed any response to changes in conditions that would suggest collisional stimulation of emission. Hence we conclude that the emission of these lines is governed by their true radiative transition probabilities. Typical intensities were, for the four lines (in units of photons per cubic centimeter·second): 3.3×109, 1.0×1010, 4.0×1010, and 1.8×109, respectively. The ratio of intensities of 5577 and 2972 Å (which have the common upper level 1 S) has a constant value of 22±2 within the range of conditions in which we can observe these lines, as compared with the theoretical value of 16 computed by Garstang. We discuss, in terms of molecular selection rules, the collisional stimulation of the line 5577 Å that is observed by others at high pressures.