Calculation of Line Widths in H2O-N2 Collisions

Anderson’s general theory of collision line broadening has been applied to ${\mathrm{H}}_2\mathrm{O}‐{\mathrm{N}}_2$ encounters. The only attractive force was assumed to be that between the ${\mathrm{H}}_2\mathrm{O}$ dipole, ${\text{μ\hspace{0.17em}=\hspace{0.17em}1.87×10}}^{\text{−18}}\hspace{0.17em}\mathrm{esu},$ and the ${\mathrm{N}}_2$ quadrupole, $q{\mathrm{N}}_2,$ an adjustable parameter. A second adjustable parameter, $b_m,$ 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 $\text{J″\hspace{0.17em}=\hspace{0.17em}13,}$ parameters $q{\mathrm{N}}_2{\text{\hspace{0.17em}=\hspace{0.17em}2.62×10}}^{\text{−26}}\hspace{0.17em}\mathrm{esu}$ and $b_m\text{\hspace{0.17em}=\hspace{0.17em}3.2}$ A which give an exact fit of the observed width of the microwave line $6_{\text{−5}}{\text{−5}}_{\text{−1}},$ 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 $\text{0.11115\hspace{0.17em}}{\mathrm{cm}}^{\text{−1}}\mathrm{\hspace{0.17em}atmos}$ for $1_1{\text{−1}}_{\text{−1}}$ to $\text{0.03200\hspace{0.17em}}{\mathrm{cm}}^{\text{−1}}\hspace{0.17em}{\mathrm{atmos}}^{\text{−1}}$ for ${14}_{\text{−13}}{\text{−13}}_{\text{−13}},$ there being a general decrease in width with increasing J, and at a given J, decreasing width with increasing τ.