Clarification of the concept of avoided crossings in the NH-bond-rupture surfaces of excited ammonia

Evleth, E. M.; Gleghorn, J. T.; Kassab, E.

doi:10.1016/0009-2614(81)85077-4

Cited by 15 publications

(6 citation statements)

References 14 publications

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“…Since the ionization from NH 3 to NH 3 ϩ comes to change the geometric structure from the C 3v symmetry to D 3h , the ionization and excitation energies of NH 3 are relatively large. Our results of NH 3 are in good agreement with the experimental 46,47,49 and theoretical 48,50,51 results. The potential energy curves for the ground and low lying excited states of the Rydberg NH 4 radical dissociating into ͑NH 3 ϩH͒ are drawn in Figure 1.…”

Section: Resultssupporting

confidence: 89%

Avoided curve crossing for the dissociation of the Rydberg NH4 radical into (NH3+H)

Park

1997

The Journal of Chemical Physics

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Section: Resultssupporting

confidence: 89%

Avoided curve crossing for the dissociation of the Rydberg NH4 radical into (NH3+H)

Park

1997

The Journal of Chemical Physics

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“…66 Alternatively, in molecular orbital rather than electronic state terms, there could be deRydbergization of a single potential energy surface as dissociation proceeds. 67 Both descriptions can lead to a representation of predissociation in NH 3, 67-69 but the single potential energy surface approach is theoretically more justified in the case of the evolution of the lowest lying singlet excited state. 70 We note that in the 10.41-10.75 eV region, Miller et al 71 found that vibrational autoionization is dominant.…”

Section: Ivb2 Nhmentioning

confidence: 99%

“…The dissociation to ground state NH 2 (X ˜) can then be considered as a homogeneous vibrational predissociation of a single state (Herzberg's case II predissociation) although Herzberg 33 treats it as a case I predissociation, involving interaction between two 1 A 00 2 states. However, only one such electronic state is expected from the pertinent electronic configurations and one must consider rather the approach involving deRydbergization of a single potential surface, 67 as discussed earlier in section IV.B.2.1. The NH 3 (A ˜) state dissociation is mainly to NH 2 (X ˜), but the proportion going to NH 2 (A ˜) via out-of-plane motion through the conical intersection increases with n 2 vibrational excitation.…”

Section: Ivd Further Remarks On Nh 3 Dissociation Mechanismsmentioning

confidence: 99%

VUV Photodissociation of ammonia: a dispersed fluorescence excitation spectral study

Leach

Jochims

Baumgärtel

2005

Phys. Chem. Chem. Phys.

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NH2 and NH transitions were identified in dispersed fluorescence spectra obtained by VUV excitation of NH3 at nine different energies between 8.266 and 15.498 eV. Fluorescence excitation (FEX) spectra between 6 and 15 eV were measured at seven specific emission wavelengths for these species. This extends the usual 11.7 eV upper limit of NH3 FEX spectra. Among the results of our work are the following: (i) a clarification of the assignment of the emission carriers; (ii) analysis of the FEX spectra of NH2(A 2A1 --> X 2B1) emission and assignment of the features to members of the npe' <-- 1a"2, nde" <-- 1a"2, nsa'1 <-- 1a"2 and nda'1 <-- 1a"2 Rydberg series transitions of NH3; (iii) new information on photodissociation processes leading to formation of NH2(A 2A1) and of NH in various excited states, in particular concerning the formation of NH (A 3pi) at 8.266 eV by dissociation of the a 3A"2 state of NH3, the existence of a potential barrier of 360 +/- 70 meV in the dissociation to form NH (c 1pi) at 9.85 eV and its formation from a non-planar state above 11.3 eV; (iv) information pertaining to the heat of formation of the NH radical, which we determine as deltaH(f,0) degrees (NH) = 3.70 +/- 0.01 eV, and to the thermochemical limits of the dissociation reactions of NH3.

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“…The key point is that the observed threshold UV photochemistries of methylamine and methanol show principally NH and OH ruptures, respectively. These processes are not those observed of molecular Rydberg states has been thoroughly dealt with by Robin.1 However, the subject of the intercorrelation of Rydberg reactant-product states is not as comprehensively discussed, and the reader is referred to a number of articles.5-8,37-39 An important point is that while low-lying valence excited states exist for larger molecular systems, smaller saturated systems (e.g., H20, NH3, CH4, alkanes) may have only Rydberg low-lying states.24, 25,[38][39][40] In particular, spectral assignments of the type, -*, -* are deceptive since a large Rydberg basis set calculation may not produce such species. At the vertical excitation geometries the * MOs may (H20, NH3, CH4)24,25,40 or may not (e.g., Cl241) be Rydberg in character.…”

Section: Preliminary Observationsmentioning

confidence: 99%

“…The above concept of MO-Rydbergization must be coupled with that of MO-dissociating states if the final state-to-state correlation is to be obtained.44 Although the avoided crossing Rydbergizations required Cl, as do ground-state bond rupture surfaces in filled shell species, the n,3s singlet NH bond rupture surface in NH3 can be qualitatively treated at the open-shell RHF level since there is a direct state-to-state correlation at the orbital-by-orbital level. 38,401 The 3s MO in NH3 will eventually de-Rydbergize and localize on the departing H atom. We will show that the overall de-Rydbergization process is 3s -*• 3s,a* -IsH.…”

Section: Preliminary Observationsmentioning

confidence: 99%

Theoretical aspects of the photochemistry of methanol, methylamine, and related materials

Kassab¹,

Gleghorn²,

Evleth³

1983

J. Am. Chem. Soc.

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The photochemistries of methanol and methylamine are computationally rationalized using ab initio methods. It is shown that the lowest excited singlet states of these and related materials are n,3s Rydberg in character. These states are computationally shown to evolve adiabatically to the valence ground states of the various radical products along the NH, CN, CO, and O H bond rupture pathways in methylamine and methanol, respectively. The N H and CN n,3s bond rupture surfaces display minima in the region of the Franck-Condon excitation geometry. The N H bond ruptures in n,3s singlet ammonia and methylamine are shown to be identical in having small activation energies. The CN excited state bond rupture shows a much larger activation energy, indicating that trialkylamines should display some photostability in the region of the 0-0 transition. In methanol, neither CO nor OH excited-state bond rupture coordinates show minima. The observed preference for O H bond rupture in the UV Photochemistry of methanol is rationalized as resulting from the lighter mass of the H atom as well as the computed more repulsive nature of the OH bond rupture. In methanol, both 1,2-and l,l-Hz molecular elimination excited-state pathways are examined. 1,2-H2 elimination is found to have a small activation energy while the 1,l-elimination is difficult. The concept of de-Rydbergization is fully developed in order to rationalize the change in electronic character occurring along these various excited state pathways.The goal of this article is to characterize theoretically the absorption threshold photochemistry of methanol, methylamine, and related small molecules. We will show that the excited states generated in the absorption threshold region are all singlet and Rydberg (n,3s) in character. We will also show that there are adiabatic surfaces which allow these Rydberg states to evolve directlv to the valence states of the fragmentation products.'Centre de Mkanique Ondulatoire AppliquEe.Pre;ious emphasis on the properties oT small-molecule excited *University of Lancaster.states has been largely spectroscopic.' Standard photochemical

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Clarification of the concept of avoided crossings in the NH-bond-rupture surfaces of excited ammonia

Cited by 15 publications

References 14 publications

Avoided curve crossing for the dissociation of the Rydberg NH4 radical into (NH3+H)

Avoided curve crossing for the dissociation of the Rydberg NH4 radical into (NH3+H)

VUV Photodissociation of ammonia: a dispersed fluorescence excitation spectral study

Theoretical aspects of the photochemistry of methanol, methylamine, and related materials

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