Exploration of the van der Waals Region of the NO A2Σ+ + N2 X1Σg+ Collision Complex.

The van der Waals (VdW) region of the potential energy surface (PES) of the collision complex of NO(A2Σ+) and N2(X1Σg+) was explored using explicitly correlated coupled-cluster methods. The Rydberg character of the NO(A2Σ+) state necessitated a sufficiently large and diffuse basis set. Basis set superposition error endemic to such systems was mitigated by the use of an explicitly correlated method in addition to a counterpoise correction, subsequent benchmarking was performed via both energetics and molecular properties such as the dipole and quadrupole moment. The method ultimately used was CCSD(T)-F12a/t-aug-cc-pVTZ, with the full VdW PES constructed through a series of three-dimensional cuts exploring the space between key orientations. A broad main minimum well was observed surrounding the linear nitrogen-to-nitrogen ("LN") orientation with a maximum depth of -239.51 cm-1 at an intermolecular separation of 4.2⁡Å. This new PES is useful for interpretation of recent molecular beam scattering experiments.