A b i n i t i o multiple root optimization MCSCF study of the C∞v/C s excitation spectra and potential energy surfaces of N2O

Abstract

This paper presents the results from extensive theoretical studies of the electronic structure for nitrous oxide. These studies have included the development of correlated ab initio MCSCF/CI wave functions for each of some 30 states, including MCSCF excited root/same symmetry calculations where necessary. Also, in the case of seven lower states, the potential energy hypersurfaces and dipole moment functions have been scanned using both MCSCF/CI and SCF wave functions. Vertical spectrum calculations are the most accurate and have been carried out at several levels of sophistication, including SCF, MCSCF, and MCSCF/CI correlation for DZ, DZ+diffuse, DZ+d, and DZ+d+diffuse one-electron bases. From all of these calculations the adiabatic excitation spectrum is established and the behavior of a number of states upon dissociation under C∞v and Cs symmetry is examined. Adiabatic correlation diagrams are then constructed to summarize many of the results and to relate them to the asymptotic spectra O(k sL) +N2 ( j sΛ) and NO( j sΛ) +N(k sL). In the light of the present work, optical and electron impact data are interpreted and assigned. It is found that each feature observed in the 4–8 eV region is supported by an electronic transition (s) allowed only under Cs symmetry. These features derive such intensity as they have in consequence of vibrational motion of the molecule in its normal, linear ground state. In distinct contrast, the features observed above 8 eV are shown to involve vertical excitations allowed under C∞v as well as Cs symmetry. Several of these transitions have not been assigned previously. For others, such as the all important D1 Σ+ state, the present results provide the necessary hard evidence for making an assignment. Also reported are correlated ab initio, DZ+d treatments for the C2v isomer 1 1A1 (1 1A′) of normal nitrous oxide, and for the O–N2 van der Waals interaction. The 1 1A1, or ‘‘ring,’’ state is shown to be bound relative to O(1D)+N2 by some 1.2 eV. The O(3P)–N2 long range 1 3Π ab initio interaction potential is reasonably well fit by an exp-6 functional form V(r)=37.757 exp(−r/0.566 569)−47.139 r−6 in a.u.

Photolysis of Nitrous Oxide Isotopomers Studied by Time-Dependent Hermite Propagation

“…The absorption is dominated by the parallel transition 2 1 A′( 1 ∆) r X1 1 A′( 1 Σ + ), with additional involvement of the perpendicular transition 1 1 A′′( 1 Σ -) r X1 1 A′( 1 Σ + ) (the symmetry species of the bent (linear) moiety is indicated). 14 While the 1 ∆ r 1 Σ + transition is electronic-dipole-forbidden, the transition becomes allowed as the molecule bends. Using molecular orbital * To whom correspondence should be addressed.…”

“…16 Hopper mapped the electronic structure of N 2 O in the early 1980s at the MCSCF/CI level. 14 For the linear C ∞ν geometry there are two low-lying electronic states, 1 Σ -and 1 ∆. The 1 ∆ state splits into the 2 1 A′ and 2 1 A′′ Renner-Teller components upon bending (C s ), while the 1 Σ -state becomes 1 1 A′′.…”

Photodissociation of N2O: Energy partitioning

“…7 Two-dimensional PESs for several singlet and triplet states of linear N 2 O were calculated by Hopper. 4 Brown et al 15 and Daud et al 16 constructed two-dimensional PESs for several low-lying singlet states. Because dissociation at 204 nmat the onset of the absorption spectrum-showed very weak vibrational excitation of N 2 , 9 the NN bond length, which changes by only 1% from N 2 O to O + NN, was fixed at the X-state equilibrium value in these studies.…”

Single-field slice-imaging with a movable repeller: Photodissociation of N2O from a hot nozzle

“…The observed initial strong increase in σ (0, v 2 , 0) is attributed to the increase in the transition dipole moment with the bending angle of the molecule. 23,27,28 The incremental change in bond angle γ is large for the first few vibrational bending levels as the molecule is linear in its ground vibrational state, but γ is expected to become smaller (yet remain positive) as v 2 increases. This is qualitatively consistent with our measurements but extending the cross section calculations beyond (0, 4, 0) to the higher vibrational levels probed by our experiment are necessary for direct comparison.…”

“…In recent years N 2 O has been subject to a number of high resolution experiments [13][14][15][16] using VMI, [17][18][19][20][21][22] as well as high level theoretical calculations. [23][24][25][26][27][28][29][30][31][32] In the most recent VMI study of Suzuki and coworkers, 22 the authors ionized individual rotational states of the N 2 photoproduct. Velocity map images showed three distinct velocities, corresponding to photodissociation of the three lowest vibrational states (0, v 2 ≤ 2, 0) of N 2 O, which were populated in the molecular beam expansion.…”