I n t r o d u c t i o nThe present communication is concerned with the problem of calculating the rotation-vibration energies and the absorption intensities of a triatomic molecule from the effective nuclear potential energy function and the dipole moment surfaces within the Born-Oppenheimer approximation (Born & Oppenheimer 1927). There are at least two astrophysical applications of such calculations: -Detailed spectra of triatomic molecules can be computed under the conditions prevailing in stellar atmospheres and compared with observed spectra. -Such spectra can also be used for constructing a wavenumber-dependent absorption coefficient which can be employed for opacity calculations as outlined, for example, by J0rgensen & Jensen (1993).In the Born-Oppenheimer approximation (Born k, Oppenheimer 1927), the rovibronic energies of a molecule are calculated in two steps: -In the first step, the nuclei are held fixed in space, and the Schrodinger problem for the electrons (which interact with the "clamped" nuclei and with each other through Coulomb forces) is solved for many different nuclear geometries. The energy eigenvalue obtained in this calculation, taken as a function of the nuclear coordinates (which we denote as R n here), is the Born-Oppenheimer potential energy function V(R"). -The second step is the solution of the Schrodinger equation for the nuclear motion,where T n is the operator representing the kinetic energy of the nuclei, ip n (R n ) is a nuclear wavefunction, and E ne is the corresponding energy eigenvalue.* Guest professor 1992-93. On leave from Physikalisch