Measurement of Transition Probabilities for O I in the Vacuum Ultraviolet

Transition probabilities for O I lines emitted in the vacuum ultraviolet were measured using a wall-stabilized arc discharge operating in a mixture of argon and oxygen. The lines were emitted from a column of plasma which was observed end-on and which was characterized by a nearly uniform temperature. Optically thin conditions were achieved by reducing the relative concentration of oxygen atoms in the discharge to levels of less than one part per million. Absolute values for the O I transition probabilities were obtained by determining the oxygen-atom density and plasma length through a measurement of the absolute intensity of the O I $\lambda =7773.4\mathrm{}$ Å line, whose transition probability is known. The following values were measured for lines in the resonance transition array: $A({}_{}{}^1{}_{}{}^{}D_2^{}{}_{}{}^{}-{}_{}{}^1{}_{}{}^{}D_2^{\mathrm{o}}{}_{}{}^{},\lambda =1152\mathrm{}\mathrm{\AA })=5.5\mathrm{}\times {10}^8$ ${\sec }^{-1\mathrm{}}$; $A({}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}-{}_{}{}^1{}_{}{}^{}P_1^{\mathrm{o}}{}_{}{}^{},\lambda =1218\mathrm{}\mathrm{\AA })=1.8\mathrm{}\times {10}^8$ ${\sec }^{-1\mathrm{}}$; $A({}_{}{}^3{}_{}{}^{}P_0^{}{}_{}{}^{}-{}_{}{}^3{}_{}{}^{}S_1^{\mathrm{o}}{}_{}{}^{},\lambda =1306\mathrm{}\mathrm{\AA })=0.66\mathrm{}\times {10}^8$ ${\sec }^{-1\mathrm{}}$; $A({}_{}{}^3{}_{}{}^{}P_{2,1,0}^{}{}_{}{}^{}-{}_{}{}^3{}_{}{}^{}S_1^{\mathrm{o}}{}_{}{}^{},\lambda =1303.5\mathrm{}\mathrm{\AA })=5.9\mathrm{}\times {10}^8$ ${\sec }^{-1\mathrm{}}$. These values are in excellent agreement with recent lifetime measurements. Existing discrepancies in the literature concerning a previous arc determination of the O I vacuum ultraviolet oscillator strengths by Boldt and Labuhn are discussed. The present method is considered to be an improvement over the method used by Boldt and Labuhn which relied, first of all, upon extrapolation techniques to reach the linear part of the curve of growth and, secondly, upon a complex calculation of the oxygen-atom number density using basic conservation equations.