Infrared spectra of the van der Waals molecule (N₂)₂

Abstract

All bound states of the (N₂)₂ dimer are calculated by solving the rovibrational problem for the rigid monomer hamiltonian, using an ab initio potential and a symmetrized product basis of angular momentum and associated Laguerre functions. Next we have evaluated the infrared line strengths for all the symmetry allowed bound-bound transitions, employing the empirical dipole function deduced from the collision induced far infrared spectrum and the N₂ multipole moment and polarizability derivatives from ab initio calculations. Thus we have generated the (N₂)₂ dimer far-infrared spectrum, corresponding to pure van der Waals vibrations and rotations, and the mid-infrared spectrum in the region of the monomer fundamental stretch (2330 cm^-1). Due to the strong anisotropy of the potential, on the one hand, but the lack of rigidness of the (N₂)₂ dimer, on the other, the spacing between vibrational levels and the shape of the rotational bands and, therefore, the appearance of the infrared spectra is very irregular.