When I learned that one of my areas of research had been selected for review at a symposium in this memorable meeting of the chemical societies of the Pacific basin nations, I, of course, felt very honored. I also felt very appreciative of the efforts of all those who have arranged it, notably, Professor Jiro Tanaka of Nagoya University, and Dr. Edward Engler of the IBM Research Laboratory at San Jose, California.

In a 1970 paper (1) I presented potential curves for Xe2+ and for the lowerenergy excited states of Xe2. These curves were based on qualitative considerations supplemented by very rough quantitative arguments. It was noted that analogous curves for the other rare-gas molecules, except He2, should all be qualitatively more or less similar. Figure 1 for Xe2+ was freshly drawn for the 1970 paper, but Fig. 2 for Xe2 was a drawing made in 1949 and recognized to be in need of several changes. These modifications were described in the paper, but will be briefly listed again here. Further, some other possible needed changes in the curves and conclusions of the 1970 paper will be discussed. In addition, some consideration will be given to radiative transition probabilities from the two lowest excited states of Ne2, Ar2, Kr2, and Xe2. The following needed changes in the 1970 paper were noted there:

(1) Previous estimates of the vertical energies of the valence-shell states of the iodine molecule are revised in the light of newer information. Correspondingly, a complete set of estimated potential curves is drawn for those valence-shell states which dissociate into ground-configuration atoms. In the light of this set of curves, conclusions in several recent papers are reviewed and in some cases revised. LeRoy's 0g+ excited state is reconsidered. Predissociations of the 2431, Π30+u(B) state are discussed. It is definitely concluded that the state mainly responsible for magnetic predissociation is the corresponding Π30−u state and not a Σ3u+(0−) state. It is, however, possible that a ∑3u+(0−) state, probably that of the 1441 configuration, makes some contribution to the magnetic predissociation near υ = 10. Spontaneous predissociation and collision-induced predissociation are also discussed. (2) Previous calculations for the estimation of the wavefunctions, relative energies, and transition probabilities from the normal state 2440, 1Σg+(X), of the several states of the 2431 configuration, are revised in the light of newer evidence. It is concluded that of the fairly strong visible absorption, perhaps 20% is due to the transition 1Πu ← X, the rest being 3Π0+u ← X and a little 3Π1u ← X. It is concluded that the 3Π0+u ← X transition moment results largely from case c mixing of 2431, 3Π0+g into X and relatively little directly from the mixing of 1441, 1Σu+ into 3Π0+u, but that a cross term arising from the joint effect of these two admixtures is also important. (3) Contrary to some writers, the conclusion that the intense uv room temperature absorption bands peaking at about 1825 Å (part of the Cordes bands) belong to the transition 1441, 1Σu+ ← X(D ← X) of the VN type, is strongly reaffirmed. The corresponding 1441, 3Σu+(1u) transition is identified with the weak I2 continuous absorption peaking near 2700 Å. Possible minor overlapping contributions from other weakly allowed transitions are discussed. The extension of the D ← X bands to longer wavelengths in high-temperature absorption is reviewed. An equation given by Wieland, aside from some uncertainty in the vibrational numbering, accurately describes the vibrational pattern of the D levels. The high-temperature absorption bands with low-frequency edges at λ 3427 and λ 3263 (Skorko bands) are, respectively, attributed to the transitions 1432, 3Π2g ← 2431, 3Π2u and 1432, 3Π1g ← 2431, 3Π1u which theoretically should be intrinsically intense like the D ← X bands. (4) Starting from semiclassical considerations in an accompanying paper on the role of kinetic energy in the Franck–Condon theory, and taking into account various experimental observations, it is concluded that the uv McLennan bands which culminate in a relatively intense series of fluctuations at about λ3250 are a part of the fluorescence spectrum resulting from excitation into vibrational levels of the D state; the resonance series at higher frequencies belongs to the same fluorescence spectrum (“primary fluorescence spectrum”). Other McLennan bands at longer wavelengths are attributed to transitions down to repulsive curves from other initial electronic states produced by collisions (“secondary fluorescence spectrum”). It is shown that the “fluctuation interval” in the λ3250 group has a magnitude, and varies with exciting frequency, in reasonable accord with the theory. From its magnitude approximate conclusions are drawn about the minimum energy and equilibrium internuclear distance for the D state potential curve. Further experimental work should be of interest. (5) The emission band systems obtained in the presence of considerable pressures of foreign gases (N2 or Ar) are discussed, and reasonable assignments for some of their upper, ion-pair type, initial states are given. In the case of the very strong region with maximum near λ 3425, proposals of Verma, Wieland, and Tellinghuisen are considered, but further work will be necessary before definite conclusions can be reached. Very likely more than one electronic transition may be involved.

This paper reviews some aspects of the theory of the interaction of electron donors and acceptors, with particular reference to 1 : 1 interactions in solution, and also seeks to clarify and broaden some current viewpoints and applications of the theory(1). The classification of donors and acceptors, and the characteristics of various types of donor-acceptor interaction pairs (including ion-pairs, H-bonded complexes, 2-way charge-transfer complexes, reaction intermediates, contact pairs, intramolecular π island interactions, etc.) are first discussed. Two sections are then devoted to the halogen complexes of n donors and of π donors. It is shown that the n donor complexes conform well to predictions of the general theory, the main point of fresh emphasis (whose importance is indicated by Hassel’s work on the geometry of solid complexes) being that some account must be taken of the participation of more than one dative resonance structure in stabilizing the normal state of most complexes. Interesting questions remain concerning the structure and charge-transfer spectra of complexes of the classical benzene-iodine type ; probable answers are discussed. The last section deals, for the interaction of neutral-molecule even-electron donors and acceptors, with potential surfaces for the normal and charge-transfer excited states in each of three limiting cases (W1 > W0, W1 ≈ W0, and W1 < W0, where W1 and W0 are the energies of the pure dative and pure no-bond structures respectively), and in each case for the two subcases of strong and weak interaction; the discussion in the third case is applicable also to compounds like NaCl, CH3NO3, (CH3)3CCl, etc. Photochemistry of contact pairs, the ionogenic effects of polar environments, and electron transfer between low-ionization-potential donors and high-electron-affinity acceptors (with possible relevance to biological systems and semi-conducting solid complexes) are briefly discussed. In discussing H-bonded complexes, new reasons favoring the importance of charge-transfer as against classical electrostatic forces are given (Sec. II).

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTMolecular Complexes and Their Spectra. IX. Infrared Absorption by Iodine in its Pyridine Complexes and in BenzeneEarle K. Plyler and Robert S. MullikenCite this: J. Am. Chem. Soc. 1959, 81, 4, 823–826Publication Date (Print):March 1, 1959Publication History Published online1 May 2002Published inissue 1 March 1959https://pubs.acs.org/doi/10.1021/ja01513a019https://doi.org/10.1021/ja01513a019research-articleACS PublicationsRequest reuse permissionsArticle Views210Altmetric-Citations43LEARN 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 InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTMolecular Compounds and their Spectra. IIRobert S. MullikenCite this: J. Am. Chem. Soc. 1952, 74, 3, 811–824Publication Date (Print):February 1, 1952Publication History Published online1 May 2002Published inissue 1 February 1952https://doi.org/10.1021/ja01123a067RIGHTS & PERMISSIONSArticle Views4754Altmetric-Citations2031LEARN 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 (2 MB) Get e-Alerts Get e-Alerts