Change of Vibrational Energy into Rotational Energy in the Nitrogen Molecule

Abstract

IT is well known that the appearance of a molecular spectrum sometimes shows a marked change with a change in the source conditions. This has been investigated in the case of the N₂ spectrum by Nakamura¹, Coster² and Feast³. Nakamura, using a low-voltage arc in nitrogen at a pressure of 30–50 cm of mercury, observed that the rotational temperature of the second positive bands is much higher in the arc than in a positive column discharge. He was able to measure rotational lines up to J = 112 in the (0,0) band. Feast used a high-tension arc in nitrogen at one atmosphere pressure and measured rotational lines up to J = 100. The average rotational temperature was about 4,000° K in the arc and 1,000° K in the positive column discharge at low pressure. He also observed that with an increase in the rotational temperature there was a decrease in the vibrational temperature. His observations were mainly confined to the (0,0) sequence which shows this change clearly. In his thesis he has given two photographs, one from the high-tension arc and the other from the positive column discharge³. The discharge spectrum shows all the bands of the (0,0) sequence up to (4,4); but, in the arc spectrum, the (1,1) and the (2,2) bands have completely disappeared and the (3,3) and the (4,4) are very much weakened.