AbstractThe electron density near the lithium nucleus in the species LiH, LiH+, Li2, Li2+, LiH2+, and Li2H+ was analyzed by transforming the SCF molecular orbitals into a sum of atomic contribnutions, for both core and valence orbitals. These “hybrid‐atomic” orbitals were used to compare: electron densities, orbital polarizations, and orbital mean kinetic energies with the corresponding lithium atom quantities. Core‐orbital electron densities at the lithium nucleus were observed to increase by up to 0.5% relative to the lithium atom 1s orbital. Lithium cores also exhibited polarization but, surprisingly, in the direction away from the internuclear region. Similar dramatic changes were seen in the electron densities of the valence orbitals of lithium: The electron density at the nucleus for these orbitals increased two‐fold for homonuclear species and twenty‐fold for heteronuclear triatomic species relative to the electron density at the nucleus in lithium atom. The polarization of the valence orbital electronic charge, in the vicinity of the lithium nucleus, was also away from the internuclear region. The mean “hybrid‐atomic” orbital kinetic energies associated with the lithium atom in the molecules also showed changes relative to the free lithium atom. Such changes, accompanying bond formation, were relatively small for the lithium core orbitals (within 0.2% of the value for lithium atom). The orbital kinetic energies for the lithium valence electrons, however, increased considerably relative to the lithium atom: By a factor of about 2 in homonuclear diatomics, by a factor of 7 in heteronuclear diatomics, and by a factor of 11 in the triatomic species. In summary, the total electronic density (core plus valence) at the lithium nucleus remained remarkably constant for all of the species studied, regardless of the effective charge on lithium. Thus, the drastic changes noted in the individual lithium orbitals occurred in a cooperative fashion so as to preserve a constant total electron density in the vicinity of the lithium nucleus. In all cases, bond formation was accompanied by an increase in the orbital kinetic energy of the lithium valence orbital. We suggest that these two observations represent important and significant features of chemical bonding which have not previously been emphasized.
All possible molecules and monopositive cations containing lithium and hydrogen, up to a total of four atoms, have been studied by ab initio calculations using SCF wave functions built from Gaussian-type orbitals. The triatomic molecules and ions Li2H, Li3, H+3 , LiH+2 , Li2H+, and Li+3 were all found to be stable, i.e., of lower energy than any possible dissociation product. The neutral molecules H3 and LiH2 were found to be unstable relative to H2+H and Li+H2, respectively. The ions H+3 and Li+3 were found to be equilateral triangles, Li2H+ was found to be a linear species, while all of the other stable triatomic species were found to be bent. The binding energies (relative to the most stable dissociation products) for the triatomic molecules and ions ranged from 4.53 eV for H+3 to 0.24 eV for LiH+2 . All of the ten possible tetra-atomic molecules and cations were found to be stable (except H4 neutral, for which no calculations were done). The lowest energy structures for LiH3 and LiH+3 consisted of planar structures with an H2 unit perpendicular to an LiH unit and having the H2 at the Li atom end. The lowest energy for Li2H2 was obtained for a planar rhombic structure, while for the corresponding cation it was obtained for a planar structure with an Li2 unit perpendicular to an H2 unit. Li3H and Li3H+ were found to have lowest energy for planar kite shaped structures with a lithium atom loosely bound to the base of a triangle formed by an Li–H–Li unit. The shapes of Li4 and Li+4 were respectively: a rhombic structure and a triangular Li+3 unit with the fourth lithium atom attached to a vertex to form a planar structure similar to H+4 . The predicted binding energies for the tetra-atomic molecules and ions ranged from 0.08 eV for LiH3 (least stable) to 1.20 eV for Li2H2 (most stable). The present work predicted for the first time a stable LiH3 neutral molecule, and stable Li2H+2 and Li3H+ cations. It also predicted for the first time that the most stable Li+4 ion corresponded to a C2v structure analogous to that of H+4 .
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTCharacteristics of an outstanding teacherW. H. Eberhardt Cite this: J. Chem. Educ. 1982, 59, 11, 963Publication Date (Print):November 1, 1982Publication History Received3 August 2009Published online1 November 1982Published inissue 1 November 1982https://doi.org/10.1021/ed059p963RIGHTS & PERMISSIONSArticle Views189Altmetric-Citations1LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts Get e-Alerts
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTTextbook errors index: Numbers 73-138W. H. Eberhardt Cite this: J. Chem. Educ. 1980, 57, 2, 129Publication Date (Print):February 1, 1980Publication History Received3 August 2009Published online1 February 1980Published inissue 1 February 1980https://doi.org/10.1021/ed057p129RIGHTS & PERMISSIONSArticle Views137Altmetric-Citations1LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (3 MB) Get e-Alerts Get e-Alerts
The MRS of IBr in the visible region of the spectrum has been studied at high resolution and a rotational and vibrational analysis is reported. The spectrum consists of short runs in J′ for several neighboring vibrational states of the mixed B, 3Π0+, and B̃′, 0+ electronic states. These results imply that only a small number of closely related rotational-vibrational states of the combined system have sufficiently long lifetimes to provide the sharp lines required for the appearance of a MRS. The values observed extend to higher energies similar results reported by Selin for the absorption spectrum.
ADVERTISEMENT RETURN TO ISSUEPREVLetterNEXTTextbook errors, No. 111: Isomers of the porphyrinsW. H. Eberhardt Cite this: J. Chem. Educ. 1973, 50, 10, 728Publication Date (Print):October 1, 1973Publication History Received3 August 2009Published online1 October 1973Published inissue 1 October 1973https://doi.org/10.1021/ed050p728.1RIGHTS & PERMISSIONSArticle Views106Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (252 KB) Get e-Alerts Get e-Alerts
The magnetically induced circular birefringence and dichroism of several bands in the electronic spectrum of ICl have been studed with a resolution of approximately 0.1 cm−1. The frequency dependence is in agreement with predictions based on the semiclassical dispersion formulas provided that each Zeeman component of a single zero-field line is treated separately. The line center is displaced by the Zeeman shift and the intensity is determined by first-order perturbation by the magnetic dipole-moment operator which mixes neighboring J states. Thus, although the qualitative aspects of the semiclassical treatment of the Faraday effect may be extended into regions of the spectrum in the immediate vicinity of sharp-line molecular spectra, the details of the spectrum depend in a very sensitive way on the molecular parameters and the rotational structure of the band.
A method is suggested for testing the reliability of the JWKB technique for the study of diatomic vibrations and the construction of potential functions. The vibrational isotope shifts are calculated from the first-order, semiclassical quantization condition and compared with those determined experimentally. Deviations which may be attributed to failure of the first-order approximation are then used to calculate the second-order correction to the phase-integral quantization condition and the potential function constructed by RKR techniques. The technique is applied to ICl and IBr where accurate data exist and the results indicate that the first-order approximation is remarkably accurate to high vibrational excitation but may fail in the energy range very close to dissociation.
Nine vibrational bands have been found in the magnetic rotation spectrum (MRS) of the 3B1u ← 1Ag transition in pyrazine near 3700 Å; no MRS was observed for the region ascribed to the 1B1u ← 1Ag transition near 3200 Å. The origin band at 3727 Å exhibits a very sharp spike of negative sign near the band center and clearly resolvable rotational structure extending into the wings. Both the location and sign of rotation of the resolved structure are consistent with a case (b) model of the triplet state. The sign of the sharp spike is not explicable in terms of this model and suggests a different coupling scheme or more subtle effects in the MRS. This study provides the first clear correlation of sign of rotation in MRS with the rotational structure of a polyatomic electronic transition.
The absorption spectrum of 2,4-di-iododecaborane-12 has been studied in solution at 25°C and as a single crystal at 77°K with polarized radiation. The lowest electronic transition is interpreted as an allowed transition in the free molecule to either a B1 or B2 excited state. The origin is probably at 21 800 cm−1; the band has an oscillator strength of 0.037 in cyclohexane. The parent compound decaborane has an origin at 31 050 cm−1 and an oscillator strength in cyclohexane of 0.10. Simple MO arguments suggest that the spectrum may be described as a transition from an essentially nonbonding orbital mostly on the iodines into a boron framework orbital similar to that responsible for the lowest excited state of decaborane itself.
The near ultraviolet absorption spectrum of decaborane has been studied in the gas from 90° to 140°C, in solution in cyclohexane and acetonitrile at 25°C, and as single crystals at 4.2°K, and evidence found for one electronic transition with origin at 3.86±0.03 ev in the gas, 3.81±0.06 ev in cyclohexane, 4.00±0.06 ev in acetonitrile, and 3.850±0.001 ev in the crystal. The existence of another excited electronic state of slightly higher energy cannot be ruled out since the absorption due to transitions to this state might be concealed by that due to the 3.85 ev transition. Assuming the absorption is due to one transition only, the transition moment and oscillator strength in cyclohexane are p2=0.21×10—16 cm2 and f=0.10, respectively. The shift of the spectrum towards the blue in the polar solvent acetonitrile relative to that in the nonpolar solvent cyclohexane indicates that the dipole moment of the excited state is less than that of the ground state. The absorption of the crystal is completely polarized perpendicular to the crystal c axis and the twofold axis of the molecule. This result implies that the excited state of the free molecule is of either B1 or B2 symmetry and the transition is allowed. No structure was observed in the gas or solution spectra, but in the crystal the electronic transition is accompanied by three totally symmetric boron framework vibrations of the excited state with frequencies 425, 390, and 135 cm—1. A detailed discussion of the wave functions and energies of the optically excited crystal states indicates that the Davydov splitting should be too small to be observed under the experimental conditions. The spectrum is entirely consistent with that expected from existent theories of the nature of electronic bonding in this molecule.
Magnetic rotation spectra have been found corresponding to the singlet-triplet transitions in formaldehyde, glyoxal, and benzoquinone. The spectrum in formaldehyde is very similar to the absorption spectrum; that in glyoxal is especially intense and exhibits some unusual peculiarities in both vibrational and rotational structure. Benzoquinone exhibits a magnetic rotation spectrum in only a single band which may be the origin of the singlet-triplet transition. No magnetic rotation spectrum was found for transitions reported to be of this type in several other substances.
The magnetic rotation spectrum of ICl corresponding to the transition 3Π1 ← 1Σ is reported and provides a classic example of the theory of the phenomenon and its application to structure analysis, isotope effects, and the determination of dissociation limits. In the region of vibrational energy in excess of 96% of the dissociation energy an anomalous drop in intensity is observed and explained only qualitatively in terms of an electronic perturbation.
Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter Facebook Reddit LinkedIn Tools Icon Tools Reprints and Permissions Cite Icon Cite Search Site Citation William G. Trawick, W. H. Eberhardt; Electronic Transitions in the Nitrite Ion. J. Chem. Phys. 1 August 1954; 22 (8): 1462. https://doi.org/10.1063/1.1740425 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAIP Publishing PortfolioThe Journal of Chemical Physics Search Advanced Search |Citation Search
A set of extended valence postulates is presented including the concept of the localized three-center bond. These postulates are applied systematically to the boron hydrides and account for their unusual geometry, their unexpected dipole moments, and the fact that they are not ``electron-deficient.''
Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter Facebook Reddit LinkedIn Tools Icon Tools Reprints and Permissions Cite Icon Cite Search Site Citation W. H. Eberhardt; On the Structure of Ozone. J. Chem. Phys. 1 October 1946; 14 (10): 641. https://doi.org/10.1063/1.1724078 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAIP Publishing PortfolioThe Journal of Chemical Physics Search Advanced Search |Citation Search
