Quantal calculations are carried out of the function of the excited 3&Pgr;u state of molecular oxygen, and the X3Jg--3&Pgr;u transition dipole moment is determined. The resulting absorption cross sections are evaluated, and it is demonstrated that absorption into the 3&Pgr;u state is not a significant source of atmospheric opacity. It is shown also that radiative association of oxygen atoms through emission from the 3&Pgr;u state is not an important source of infrared airglow.