Knowledge Bank

Collision-induced absorption spectra of $H2$ in the pure gas in its first overtone region was recorded with a 2 m cell for gas densities up to 435 amagat at 77, 201 and 295 K. The spectra consist of pure overtone ($\Delta v=2$) transitions; $O2(J)+Q0(J),Q2(J)+Q0(J),S2(J)+Q0(J)$ and $Q2(J)+S0(J)$, and fundamental ($\Delta v=1$) transitions $O1(J)+Q1(J),Q1(J)+Q1(J)$ and $S1(J)+Q1(J),J$ varying from 0 to $3.a$. Birnbaum-Cohen (BC) lineshape $functionb$ was used in the profile analysis of the observed spectra. It is found that the isotropic overlap contribution to the first overtone band is negligible and the anisotropic overlap contribution to the absorption of pure overtone transitions is negative. The latter was estimated by effectively scaling down the values of the quadrupolar matrix elements of the pure overtone transitions. Details of the results of the profile analysis, parameters of the BC lineshape function and binary and ternary absorption coefficients will be presented.