Bound–bound A 2Σ+–X 2Π transition of NO–Ar van der Waals complexes

Abstract

The bound–bound excitation spectrum of the NO–Ar van der Waals complex associated with the NO A 2Σ+–X 2Π transition has been measured by the resonance enhanced two-photon ionization (RE2PI) method using a time-of-flight (TOF) mass spectrometer. The van der Waals bands characterized by red-shaded rotational contours present no regularity in the progression. The photodissociation action spectra obtained by probing the NO A 2Σ+(v′=0, N′=1–8) products have also been measured, and the binding energies (D0) of the complex in the A 2Σ+ and X 2Π states are determined as 44 and 88 cm−1, respectively. The action spectrum corresponding to the NO A 2Σ+(v′=0, N′=1 and 2) product shows several shape resonance peaks, which implies that the intermolecular potential between NO A 2Σ+ and Ar has a potential barrier of about 24 cm−1.

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

“…The first investigation of the bound-bound à 2 ⌺ ← X 2 ⌸ transition was of quite low resolution but revealed that structure was observable. 7 Subsequent studies with increased resolution 8,9 revealed several bands assignable to vibrational modes. 9 The NO-Ar à − X origin was determined as 44 242.4 cm −1 and this, along with measurements of the dissociation onset, allowed à and X state dissociation energies of 44 and 88 cm −1 , respectively, to be obtained, 8 although, as discussed below, these values have recently been called into question.…”

“…7 Subsequent studies with increased resolution 8,9 revealed several bands assignable to vibrational modes. 9 The NO-Ar à − X origin was determined as 44 242.4 cm −1 and this, along with measurements of the dissociation onset, allowed à and X state dissociation energies of 44 and 88 cm −1 , respectively, to be obtained, 8 although, as discussed below, these values have recently been called into question. 10 The identification of the features observed in the bound-bound à − X spectrum was achieved through the enhanced quality of later resonance enhanced multiphoton ionization ͑REMPI͒ experiments.…”

“…The authors rationalize this behavior as being similar to the rotational rainbow phenomenon observed in inelastic collision experiments. 13 Tsuji et al 8 investigated the onset of dissociation by measuring action spectra for several NO N states. A significant outcome of their work was the observation of resonance features above dissociation for N =1,2.…”