Calculation of Line Widths in H2O-N2 Collisions

Abstract

Anderson’s general theory of collision line broadening has been applied to H2O-N2 encounters. The only attractive force was assumed to be that between the H2O dipole, μ = 1.87×10−18 esu, and the N2 quadrupole, qN2, an adjustable parameter. A second adjustable parameter, bm, the distance of closest approach, includes the effects of all other forces. The IBM 704 was used in the calculation. Effects of varying the parameters were noted for a number of lines, and in the final calculation, which yielded the widths of all significant type B transitions up to J″ = 13, parameters qN2 = 2.62×10−26 esu and bm = 3.2 A which give an exact fit of the observed width of the microwave line 6−5−5−1, were adopted. The temperature dependence of the line width over the range 220–2400 °K, and the effects of vibration-rotation interactions were also calculated. At 300 °K widths vary from 0.11115 cm−1 atmos for 11−1−1 to 0.03200 cm−1 atmos−1 for 14−13−13−13, there being a general decrease in width with increasing J, and at a given J, decreasing width with increasing τ.