A new potential energy surface for OH(A 2Σ+)-Kr: The van der Waals complex and inelastic scattering J. Chem. Phys. 137, 154305 (2012); 10.1063/1.4757859Calculation of the structure, potential energy surface, vibrational dynamics, and electric dipole properties for the Xe:HI van der Waals complexWe have estimated the potential curves of the Mg(3s3 p)•He͓ 3 ⌸͔, Mg(3p3 p)•He͓ 3 ⌺ Ϫ ͔, Mg ϩ (3s)•He͓ 2 ⌺ ϩ ͔, Mg ϩ (3p)•He͓ 2 ⌸͔, and Mg ϩ2 (2p 6 )•He͓ 1 ⌺ ϩ ͔ van der Waals states by means of ab initio calculations. Similar to the analogous doubly excited states of MgNe, MgAr, and MgKr, the Mg(3p3p)•He͓ 3 ⌺ Ϫ ͔ state is found to be unusually strongly bound, D e ϭ2386 cm Ϫ1 , a bond strength which is an astounding 165 times that of the singly excited Mg(3s3 p)•He͓ 3 ⌸͔ state and 35 times that of the Mg ϩ (3s)•He ion. The strong bonding is attributed primarily to the lack of a Mg(3s) electron, so that all the attractive forces can extend to smaller internuclear distances because there is no Mg(3s)/He(1s) repulsion. In fact, the Mg(3p3 p)•He͓ 3 ⌺ Ϫ ͔, Mg ϩ (3p)•He͓ 2 ⌸͔, and Mg ϩ2 (2p 6 )•He͓ 1 ⌺ ϩ ͔ states have quite similar bond energies and bond lengths, indicating that for RGϭHe, the primary attractive force in all these states is the ion/induced-dipole interaction of the ''Mg ϩ2 /He'' core. This is consistent with the fact that the bond energy of the Mg(3p3 p)•He͓ 3 ⌺ Ϫ ͔ state is more than four times greater than that of the Mg(3p3p)•Ne͓ 3 ⌺ Ϫ ͔ state, where there is substantial Mg(3p)/Ne(2p) repulsion not present in the Mg(3p3p)•He͓ 3 ⌺ Ϫ ͔ state.

Electron states of benzene-Br2 donor-acceptor complex: HeI photoelectron spectroscopy and ab initio molecular orbital study

We have estimated the potential curves of the Mg(3s2)⋅Ne(1Σ+), Mg(3s3p)⋅Ne(3Π,3Σ+), Mg(3p2)⋅Ne(3Σ−), Mg+(3s)⋅Ne(2Σ+), Mg+(3p)⋅Ne(2Π), and Mg+2(2p6)⋅Ne(1Σ+) van der Waals states by means of ab initio calculations. Similar to the analogous doubly-excited states of MgAr and MgKr, the Mg(3pπ3pπ)⋅Ne(3Σ−) state is found to be unusually strongly bound, De=548 cm−1, a bond strength which is more than 20 times that of the singly-excited Mg(3s3pπ)⋅Ne(3Π) state and even more than three times that of the Mg+(3s)⋅Ne ion. The strong bonding is attributed primarily to the lack of a Mg(3s) electron, so that all the attractive van der Waals forces can extend to smaller internuclear distances because there is no Mg(3sσ)/Ne(2pσ) exchange repulsion.

The first metastable valence excited states and the first Rydberg states of the MgKr and MgXe molecules have been characterized by resonance two-photon photoionization (R2PI) spectroscopy. The Mg(3s3p 3PJ)⋅RG(3Π0+,0−) metastable states, produced by expanding the products of a laser-ablated magnesium rod in Kr/Ar or Xe/Ar gas mixtures into a supersonic expansion, were excited by a dye laser pulse to several vibrational levels of the Mg(3s4s 3S1)⋅RG(3Σ+) Rydberg states, with detection by ionization with a second dye laser pulse. Spectroscopic constants, bond energies, and bond lengths are reported for both states of MgKr and MgXe. The 3Σ+ Rydberg states are much more strongly bound than the lower 3Π0− valence states, and in fact are essentially as strongly bound as the ground states of the analogous MgRG+ ions, characterized previously in the same apparatus. This clearly indicates that the RG atoms can readily penetrate the diffuse Mg(4s) Rydberg electron cloud. The interesting and unusual spin–orbit and “spin–spin” effects observed are attributed to mixing of some RG character into wave functions of predominantly Mg* excited state character. Bonding and spin–orbit interactions in the MgAr, MgKr, and MgXe first triplet metastable and Rydberg states are discussed.

It has been shown, using a “model-potential” analysis, that −Cn/Rn dispersive terms can be an important part of the physical bonding in M+/Rg complexes (M+=atomic metal ion, Rg=rare gas atom) for M+ ions with large, polarizable outer-shell electron clouds. The model potential equation consists of all attractive terms (accurately calculated or estimated) out to 1/R8, as well as an Ae−bR repulsive term. From known De, Re, and ωe values, and the first and second derivatives of the model potential, the repulsive constants A and b as well as the effective charge Z of M+ in a particular M+⋅Rg electronic state, can be determined. For the typical M+⋅Rg states considered here, Z=1.02±0.07, indicating that no extra “chemical” effects are necessary to explain M+/Rg bonding. Furthermore, the trends in the derived Ae−bR repulsive curves make good qualitative sense. A term-by-term analysis for M+⋅Rg states where the M+ ion is small and unpolarizable [such as Na+(2p6)⋅Rg] shows that −Cn/Rn terms contribute only a few percent to the bond strengths, while for M+⋅Rg states where M+ is large and polarizable [for example, Mg+(3s)⋅Rg], the −CnRn terms can contribute on the order of 40%–50% to the bond strengths, thus rationalizing semiquantitatively several heretofore puzzling De, Re, ωe comparative values.