摘要:

not available

ISSN:0008-4042    

DOI:10.1139/v58-001

出版商:NRC Research Press    

年代:1958

数据来源: NRC

摘要:

The present and prospective rapidly increasing usefulness of good LCAO-MO calculations on the electronic states of simple molecules in the interpretation of observed excited states is pointed out. As examples, the observed and predicted states of, in particular, the π3π configurations of N2and CO are compared with those of C2H2and HCN and with those of CO2and CS2. Further, the results of LCAO-SCF calculations on CO2and on O3are surveyed, and it is shown how these can be helpful in interpreting and understanding the ground and excited states of AB2(expecially AO2) molecules in general. A new interpretation of the so-calledd3П state of CO as a casebπu3πg,3Δustate is proposed. Tentative interpretations of some of the ultraviolet absorption spectra of C2H2, HCN, and of a number of AB2molecules are reviewed or suggested, including some discussion of the shapes of excited states. The AB2discussion is a revision of one given earlier. Finally, following up a suggestion of Coon, it is pointed out that there exists strong evidence for slightly unequal A—O distances in certain excited states of C1O2and SO2

ISSN:0008-4042    

DOI:10.1139/v58-002

出版商:NRC Research Press    

年代:1958

数据来源: NRC

摘要:

The electron distributions in the ground states of C2H2, HCO, and NH2, and in one excited state of each species, have been considered by transforming the simple molecular orbitals into equivalent ones. In the light of these considerations, the shapes and dimensions of the above species in these states have been discussed. It is found that a considerable degree of understanding can be achieved though there is uncertainty in the interpretation in some cases.

ISSN:0008-4042    

DOI:10.1139/v58-003

出版商:NRC Research Press    

年代:1958

数据来源: NRC

摘要:

Long path length, high resolution spectra in the near ultraviolet of H2CO and D2CO at −78 °C. have been obtained, and further strong evidence in support of a non-planar excited state is presented. The double-headed bands to the long wavelength side of the singlet–singlet system are shown to belong to the singlet–triplet transition. A vibrational analysis and partial rotational analysis shows the excited triplet state to be very similar to the excited singlet state. The larger C—O stretching frequency in the triplet state may characterize the multiplicity of these states in the simple aliphatic aldehydes and ketones. It is found that the C—O bond order in both states is very nearly 1.5, and striking similarities between the bonding in these states and the C—O bonding in formic acid are pointed out. The similarity between the singlet and triplet excited states may not extend to chemical behavior because of spin correlation rules, but there are no general reasons why the triplet state should be more reactive than the singlet.

ISSN:0008-4042    

DOI:10.1139/v58-004

出版商:NRC Research Press    

年代:1958

数据来源: NRC

摘要:

The ionization of the molecules of hydrogen fluoride, hydrogen iodide, water, hydrogen sulphide, and ammonia, by essentially monoenergetic electrons, has been studied in a mass spectrometer. The various excited states of the molecular ions of these compounds have been observed and the corresponding energy levels of the ions have been measured. The results are interpreted in terms of the electronic structures of these molecules as given by molecular orbital theory.

ISSN:0008-4042    

DOI:10.1139/v58-005

出版商:NRC Research Press    

年代:1958

数据来源: NRC

摘要:

The electronic absorption spectra of single crystals of toluene, dibenzyl, diphenylmethane, and biphenyl have been photographed at 20 °K. using polarized light in the range 3000 to 2500 Å. The fluorescence spectrum of biphenyl has also been examined. This is the first time that the excited states of biphenyl analogous to theB2ustate of benzene have been observed. The main features of the spectra are similar for all four compounds, and the differences may be understood in terms of the weak coupling between the benzene rings of the "double molecules".

ISSN:0008-4042    

DOI:10.1139/v58-006

出版商:NRC Research Press    

年代:1958

数据来源: NRC

摘要:

The theory of the transfer of electronic energy between two molecules, or between two parts of a "double molecule", is discussed for the case in which vibrational quanta are present. The results are obtained for two limiting cases of weak and strong electronic interaction. Some of the phenomena occurring in the intermediate region are discussed qualitatively. With the aid of these results the spectra of biphenyl, diphenylmethane, and dibenzyl have been analyzed, and the electronic energy exchange parameter has been determined for each. These data are compared with similar data on durene crystal and the paracyclophanes. The electronic energy exchange parameter is given approximately correctly by considering the interaction of electronic transition dipoles except for very close and for very distant molecules.

ISSN:0008-4042    

DOI:10.1139/v58-007

出版商:NRC Research Press    

年代:1958

数据来源: NRC

摘要:

The fundamentals of diabatic reactions are briefly reviewed. The two important types of radiationless transitions at the crossover region of two potential surfaces are considered kinetically and rate formulations are given. The first type involves an appreciable activation energy in excess of the heat of reaction. The second does not. The reaction velocity is formulated using the absolute rate theory where the transmission coefficient is interpreted in terms of the Landau–Zener probability approximation. The over-all rate of a sequence of reactions is treated in accordance with the principle that resistances in series are additive. If the second in a sequence of two reaction steps involves a negative activation energy and is slow because of failure to cross to the new surface the resultant repeated passage through the crossover region requires a special formulation of the transmission coefficient, which is given. Whether this transmission coefficient influences the over-all rate or not depends on whether or not it belongs to the rate-determining step.Quenching reactions are classified in terms of the number of free valences involved, an electron being excited from a saturated molecule conferring radical-like properties on the excited molecule. Excited odd-electron molecules will attract at considerable distances without appreciable activation energy.The transmission coefficient is discussed in terms of recruitment factors for cases in which the products of a reaction are out of equilibrium.Hot positive ions resulting from mass spectrographic reactions are indicated as another example of diabatic reactions, and a procedure for treating these by the activated complex theory is briefly mentioned.

ISSN:0008-4042    

DOI:10.1139/v58-008

出版商:NRC Research Press    

年代:1958

数据来源: NRC

摘要:

The various electronically-excited states of oxygen atoms and molecules are briefly considered. Certain reactions involving some of these electronically-excited species are then discussed with reference to the experimental evidence and to the potential-energy surfaces on which they occur. In the case of the mercury-photosensitized formation of ozone from oxygen it is concluded that both experimental evidence and theoretical arguments point to the fact that the oxygen molecule initially formed is in an excitedstate. Consideration is also given to the mechanism of formation of O2* in the carbon monoxide flame and in other flames. The reactionsandare also discussed briefly.

ISSN:0008-4042    

DOI:10.1139/v58-009

出版商:NRC Research Press    

年代:1958

数据来源: NRC

摘要:

A study has been made of the reaction of Hg2026(3P1) atoms, photoexcited in natural mercury vapor; with a number of substrates which form solid mercury compounds in mercury photo-sensitization. Some data are also given for reactions initiated by Hg1986(3P1) atoms. The solid mercury compounds formed were examined for enrichment in the isotope initiating the reaction. Such enrichment would be evidence for the primary formation of the mercury compound.Three HgO-forming substrates were studied: water vapor, nitrous oxide, and oxygen. The Hg2Cl2-forming substrates studied included hydrogen chloride, methyl chloride, methylene chloride, chloroform, carbon tetrachloride, isopropyl chloride, and boron trichloride. One Hg2Br2-forming substrate was examined—isopropyl bromide.Among the HgO-forming substrates only water vapor gave enrichment in Hg202in the HgO product. The Hg202content of the oxide was found to vary from 32 to 35%, depending on reaction conditions, compared to a natural abundance of 29.6%. With water vapor – butadiene mixtures, oxides containing as high as 90% Hg202were obtained. Similar enrichment factors were obtained for Hg1986(3P1) reactions.Hydrogen chloride and the alkyl chlorides yielded calomels containing a maximum of 45% Hg202. Methyl chloride gave similar enrichment factors in Hg198for the Hg1986(3P1) reaction. The calomel formed in the boron trichloride reaction showed no enrichment.Addends such as butadiene and benzene, when added to hydrogen chloride, increased the Hg202enrichment from 45% to 60%.For those reactions which yield mercury compounds enriched in the initiating mercury isotope, evidence is presented for a single primary process. Failure to obtain pure isotopes is attributed to exchange reactions with adsorbed natural mercury during recovery of the enriched mercury from the product. It is postulated that the addends react with the mercury product and reduce chemisorption of natural mercury on the product.The significance of these findings in the mechanisms of the reactions studied is discussed.

ISSN:0008-4042    

DOI:10.1139/v58-010

出版商:NRC Research Press    

年代:1958

数据来源: NRC