Interaction of NO(A Σ2+) with rare gas atoms: Potential energy surfaces and spectroscopy

Abstract

We present the results of an ab initio study of the interaction of electronically excited NO(A (2)Sigma(+)) with rare gas (Rg) atoms. The bound states of each NO(A)-Rg species are determined from potential energy surfaces calculated at the RCCSD(T) level of theory. Making use of the NO(X (2)Pi)-Rg vibrational wavefunctions, we then simulate electronic spectra. For NO-Kr and NO-Xe we obtain good qualitative agreement with the previously published experimental spectra. For NO-Ar, the shallowness of the surface gives rise to agreement that is less satisfactory, but a global scaling provides better qualitative agreement. The assignment of the spectra is far from straightforward and is only possible with guidance from the calculated energies and wavefunctions of the energy levels of the complex. Previous assignments are discussed in the light of this conclusion.

Modelling excited states of weakly bound complexes with density functional theory

“…31 In particular, B3LYP-D3 calculations predicted a minimum energy structure with a Ar-N-O angle of 30 o , whereas high level calculations and experiment find the angle to be 0 o . [45][46][47] A further shallow minimum is predicted for a Ar-N-O angle of 180 o , in agreement with experiment and previous calculations. [45][46][47] This is illustrated in Figure 7 that shows the interaction potential at the B3LYP-D2 level, which closely resembles the B3LYP-D3 one.…”

“…[45][46][47] A further shallow minimum is predicted for a Ar-N-O angle of 180 o , in agreement with experiment and previous calculations. [45][46][47] This is illustrated in Figure 7 that shows the interaction potential at the B3LYP-D2 level, which closely resembles the B3LYP-D3 one. Also shown is an analogous potential energy surface computed with B3LYP-D2 with modified (increased by a factor of 2 for nitrogen and oxygen) van der Waals radii.…”

The dissociation of NO–Ar(Ã) from around threshold to 200 cm−1 above threshold

“…Recent calculations 23 confirm that the NO-Ar X state has a "T" structure, 3 while the à state is near linear. 6 The NO-Ar bond length is substantially increased from the X to à states. 3,6,23 There is, therefore, poor overlap between the ground vibrational levels in the two electronic states.…”

“…In contrast, the à state is linear, 4,5 with the most recent results revealing that the argon is situated adjacent to the nitrogen atom. 6 Because of the large geometry change between the X and à states, transitions to the bound region near the origin are very weak and it was some time before they were observed. The first investigation of the bound-bound à 2 ⌺ ← X 2 ⌸ transition was of quite low resolution but revealed that structure was observable.…”

“…4,11 However, a recent report has found that the previous assignments of the spectral features are incorrect. 6 These authors suggest that a quantitative fit of the major spectral features may be achieved by application of scaled results of their theoretical model, and that this should be the focus of future work. We expect that the correct assignment of the NO-Ar spectrum will be determined in due course.…”