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Published August 15, 1929 | public
Journal Article Open

The influence of foreign gases on the intensities of the magnesium resonance lines 4571 and 2852


The Mg line 4571, 31S-33P1, is very weak in the arc while 2852, 31S-31P, is very intense. The life of the 33P1 state is calculated to be 4×10^(-3) sec., while 31P has a life of 3×10^(-9) sec. Collisions of second kind between excited Mg atoms reduce intensity of 4571 in the arc. At a vapor pressure of 10^(-4) mm, the time between collisions of the Mg atoms is 10^(-3) sec. The 4571 line should appear strong at this or lower vapor pressures. Vapor from solid Mg metal at 500°C was excited in an evacuated tube by an electrodeless short-wave discharge. The 4571 line appeared in the discharge as a fairly prominent line. Effect of foreign gases on 4571. The noble gases enhanced this line, the intensity relative to the triplet 3838 increasing up to about 20 mm in argon and 10 mm in neon and helium and then remaining practically constant. At these pressures, argon increased the line 100 times, Ne about 70 times, and He about 40 times. N2 and CO increased 4571 up to the limit of pressure, about 2 mm, at which the discharge could be operated. H2 caused a slight increase at a pressure of about 2 mm. Intensity-pressure curves for noble gases have been reproduced theoretically, proving the assumption that excited Mg atoms suffer collisions of the second kind with the walls, and that action of a noble gas in enhancing the 4571 line is due entirely to the slowing up of diffusion of Mg atoms in 23P1 state to the walls, and to its inefficiency in causing collisions of the second kind with excited Mg atoms. Effect of foreign gases on 2852. All gases reduce 2852 and all singlets terminating on the 31P level. Increasing pressure of H2 reduces 2852 faster than the singlets. Dissociation of the H2 molecules by Mg atoms in 31P state reduces radiation from that state.

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©1929 The American Physical Society. Received 29 June 1929. In conclusion the author desires to thank Professor I. S. Bowen for his many suggestions and advice in interpreting the experimental results. He also wishes to thank Dr. W. V. Houston for assistance in the mathematical work and Dr. M. Muscat for assistance in the experimental work.


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