Ground states, spectroscopic constants

J.M.L. Martin, The ground-state spectroscopic constants of Be2 revisited, Chem. Phys. Lett. 303 (1999) 399. 

Han Y-K, Hirao K (2000) On the ground-state spectroscopic constants of H2. J Chem Phys 112 9353-9355... 

No thermochemical measurement of the enthalpy of formation has been made. The selected value, AjH (BeBr, g, OK) = 30.0 10.0 kcal mol", Is obtained from an analysis of spectroscopic data. The adopted values for the ground state vibrational constants give... 

A linear Birge-Sponer extrapolation of the ground state vibrational constants leads to D"(LBX) = 4.90 eV. This value can be refined by taking into account the ionic character of the P-F bond. Using relationships developed by Hildenbrand (1.), we adjust the value of D"(LBX) to obtain D" = 4.25 eV. A similar treatment of spectroscopic data (5) for related molecules (AIF, SiF, and... 

The ground state vibrational constants have not been determined experimentally. O Hare (8) computed Hartree-Fock total energies for the ground states of NF, SiF, PF, and SF and derived spectroscopic constants for each monofluoride by a Dunham analysis. He adjusted the computed values for SF for differences found between calculated and experimental data for the other three monofluorides. We adopt his predicted vibrational constants along with his computed value for a. We do not include the rotational and vibrational constants (4, 5) for the A state since they have a negligible effect. 

The new procedure permits for the first time the practical estimation of reliable near-rg structures for polyatomic organic molecules fi-om gas-phase spectroscopic ground state rotational constants. Along with gas electron diffraction and modem high-quality... 

If the metal centers contain several unpaired electrons, in principle each unpaired electron on one subunit can couple with each unpaired electron on the other unit if a bridging ligand orbital exists that overlaps with both metal orbitals involved. As described in Section 2.42.2 the corresponding superexchange pathway is mediated by CT, MMCT, and DCT states, and spectroscopic information from the CT spectrum can be used to determine the relative contribution of this specific pathway to the cumulative ground-state coupling constant... 

The complex Pd2(dba)3 in solution shows electronic absorption bands at 350, 380, and 545 nm. The band at 350 nm is due to an intraligand charge transfer transition. The band at 380 nm is due to an intermetallic da pa transition, and the lowest energy band at 545 nm is due to an MLCT transition. " The triplet emission from this complex is observed at 730 nm. By comparison, the absorption bands for Pt2(dba)3 are found at 350,400, and 620 nm, respectively, and the triplet emission is observed at 800 nm. An analysis of the ground state spectroscopic parameters reveals that both the palladium and the platinum complexes have only weak intermetallic interactions. For Pd2(dba>3 the intermetallic stretching frequency V (M-M) is found at 76 cm , which corresponds to a force constant of 0.18 mdyn A By comparison the corresponding stretching frequency in Pt2(dba)3 is found at 72 cm" which corresponds to a force constant of 0.30 mdyn A" when the mass difference is taken into consideration. ... 

A number of MO calculations has been carried out, and these have had mixed success in predicting chemical reactivity or spectroscopic parameters such as NMR chemical shifts and coupling constants. Most early calculations did not take into account the contribution of the sulfur 3d-orbitals to the ground state, and this accounts for some of the discrepancies between calculations and experimental observations. Of the MO methods used, CNDO/2 and CNDO/S have been most successful the INDO approximation cannot be used because of the presence of the sulfur atom. 

Ground-state effects, i.e., the effects on the bond lengths and angles, stretching and bending force constants, and other spectroscopic properties of the other ligands. 

The CPF approach gives quantitative reement with the experimental spectroscopic constants (24-25) for the ground state of Cu2 when large one-particle basis sets are used, provided that relativistic effects are included and the 3d electrons are correlated. In addition, CPF calculations have given (26) a potential surface for Cus that confirms the Jahn-Teller stabilization energy and pseudorotational barrier deduced (27-28) from the Cus fluorescence spectra (29). The CPF method has been used (9) to study clusters of up to six aluminum atoms. 

Schwerdtfeger, P., Fischer, T Dolg, M Igel-Mann, G., Nicklass, A., Stoll, H. and Haaland, A. (1995) The Accuracy of the Pseudopotential Approximation. 1. An Analysis of the Spectroscopic Constants for the Electronic Ground States of InCl and InCh. Journal of Chemical Physics, 102, 2050-2062. 

The recent time-resolved spectroscopic studies described above (Sections 2 and 3) identify the charge-transfer excitation (/n cr) of aromatic EDA complexes with various types of acceptors (A) to their ion-radical pairs [ArH+-,A ] (Mataga, 1984 Hilinski et al., 1984 Jones, 1988). Such electronic transitions in weak EDA complexes, like those of the halogen acceptors, are mainly associated with the excited states, such as in (32), since the variations in the ground state are minor owing to formation constants K that are not strongly dependent on the arene donor (Briegleb, 1961, pp. 106 ff.). 

Conventional absorptiometric and fluorimetric pH indicators show a shift of band positions in absorption and emission spectra between the protonated and deprotonated forms. This feature allows the spectroscopic measurement of the acid dissociation constant in the ground state, Ka, and also the evaluation of the dissociation constant in the excited state, Ka (Eq. (5.5)), from the Forster cycle under the assumption of equivalent entropies of reaction in the two states.<109 112)... 

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