We have built new global fits for the ground state potential energy surfaces (PES) of N₂–H₂ and N₂–N₂ complexes using ab initio perturbative and supermolecular methods. The analytical expressions used in the four-dimensional fitting procedure require the knowledge of the multipole moments, the static and dynamic multipolar polarizabilities of each monomer, from which long-range electrostatic, induction and dispersion coefficients are evaluated. In agreement with previous work, we have found the most stable conformation of N₂–H₂ to be linear and that of N₂–N₂ to have a 45/50° canted parallel shape. The quality of present PESs have been checked by comparing between calculated and experimental second virial coefficients and integral scattering cross-sections, which are found to be in good agreement.

The collision-induced rotational translational spectrum of gaseous N₂ has been measured in the temperature range 228–343 K at six different temperatures. The measurements were made with a Fourier transform spectrometer in the 25 to 360 cm⁻¹ region and at 15.1 and 84.2 cm⁻¹ with far infrared (FIR) laser. Previously obtained microwave data at 2.3 and 4.7 cm⁻¹ have been used in defining the complete spectrum. Using a recently developed theory for quadrupolar-induced absorption, we find that the calculated quadrupole moment is independent of temperature and has a magnitude in close agreement with the recommended values of several other workers; i.e., Q = 1.46 B. The calculated value depends on the particular form of the intermolecular potential and this dependence is examined in some detail. A contribution to the absorption originating primarily from hexadecapolar and overlap induction has been observed in agreement with theoretical estimates and leads to an estimated value for the hexadecapolar moment φ=3.4*10^-42 esu cm⁴.