Collision-induced absorption in the a(1)Delta(g)(v '=0) <- X-3 Sigma(-)(g)(v=0) transition in O-2-CO2, O-2-N-2, and O-2-H2O mixtures

When O-2 is perturbed by collisions with other molecules, the weak spin-for bidden magnetic dipole transition a(1)Delta (g)- X(3)Sigma (-)(x) shows a b road continuum absorption underlying the sharp lines. This collision-induce d enhancement absorption plays a role in the Earth's atmosphere and much ex perimental work has been carried out to measure the binary absorption coeff icient with different perturber gases. Recent work on the upsilon'= 0 <-- v = 0 band in O-2-CO2 Mixtures yielded a value for the coefficient that was approximately three times that of earlier measurements on O-2-N-2, mixtures . In the present note, we calculate the absorption theoretically assuming t hat the long-range quadrupole-induced dipole mechanism is dominant. Using e xperimental polarizability matrix elements Of CO2 and ab initio results in the literature for the quadrupolar transition matrix element for O-2, we fi nd good agreement for O-2-CO2 mixtures without any adjustable parameters. T he agreement for O-2-N-2 is less good, and because of the much smaller pola rizability of N-2 than Of CO2 We suggest that one has to include a short-ra nge component in addition to the long-range one treated here. We also calcu late the binary absorption coefficient for O-2-H2O, for which no experiment al data are available, and we synthesize the corresponding spectrum for use in atmospheric modeling. (C) 2001 Academic Press.