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M. Leleyter - One of the best experts on this subject based on the ideXlab platform.

  • Electronic structure of small fluorocarbon clusters FpCn (p =1, 2 ) observed in secondary ionic mass spectrometry (SIMS). II. Electronic populations and F-C bonding
    'EDP Sciences', 2026
    Co-Authors: M. Leleyter
    Abstract:

    A CNDO Calculation is used to interpret from a linear chain model the alternations in the emission intensities of secondary FpC± n ions (p = 1, 2) with enhancements of FpC+ 2k+1 and FpC-2k ions. The Calculation shows that the strong even-odd effect arises from the fact that the Fermi level (« HOMO ») of the clusters, assumed to be linear Cn chains with one or two F atoms related to one or both ends of the chains, falls into a band of degenerate π levels. The study of the charge oscillations throughout the chains shows that they are directly related to the carbon atom number parity and therefore to the filling of the Fermi level : there are damped periodic oscillations only for the most stable clusters ; in the other cases the charges do not show any periodic behaviour. The distribution of the charges gives interesting information on the F-C bond too and points out that the strong F electronegativity plays an essential role.On utilise un calcul CNDO pour interpréter à partir d'un modèle de chaîne linéaire les alternances dans les intensités d'émission secondaire des ions FpC±n (p =1, 2), avec renforcement des ions FPC+2k+1 et FPC- 2k. Le calcul montre que le très fort effet « pair-impair » provient du fait que le « niveau de Fermi » (« HOMO ») des agrégats supposés être des chaînes linéaires Cn avec un ou deux atomes de fluor liés à l'une ou aux 2 extrémités des chaînes, tombe dans une bande de niveaux π dégénérés. L'étude des oscillations de charge le long de la chaîne montre qu'elles sont directement liées à la parité du nombre d'atomes de carbone et par suite au remplissage du niveau de Fermi: il y a des oscillations pseudo-périodiques uniquement pour les agrégats les plus stables ; dans les autres cas, les charges ne montrent plus de comportement périodique. La distribution des charges donne aussi d'intéressantes informations sur la liaison F-C et met en évidence le fait que la forte électronégativité du fluor joue un rôle essentiel

  • Electronic structure of small fluorocarbon clusters FpCn (p = 1, 2) observed in secondary ionic mass spectrometry (SIMS). I. Stabilities
    'EDP Sciences', 2026
    Co-Authors: M. Leleyter
    Abstract:

    The intensities of emission of FpC+n(p = 1-4) and FpC-n (p =1, 2) secondary ions given by a target made of teflon (polytetra-fluoroethylene) under a primary bombardment of 6.5 keV Ar+ ions, show a very strong even-odd effect according to the parity of the number n of carbon atoms. Maxima occur when n is odd for FpC+n (p = 1-3) and when n is even in the other cases (p = 4 ; negative ions). The alternations of F pC+n and FpC-n (p = 1, 2) are interpreted with a CNDO Calculation by means of the model of the linear Cn chain similar to the Pitzer and Clementi model. It is then found that the stabilities of the linear clusters are the greatest for FC+2k+1, F2C +2k+1 and for FC- 2k and F2C-2k ions. This agrees with the « correspondence rule » between the emissions of various ions and their stabilities and electronic properties. Besides, in the case of F2C n chains, the Calculation shows that the disymmetrical isomers are in the best agreement with the experimental data.Les intensités d'émission des ions secondaires FpC+ n (p = 1-4) et FpC-n (p =1, 2) émis par une cible de téflon (polytétra-fluoroéthylène) sous bombardement primaire par des ions Ar+ de 6,5 keV, présentent des oscillations très marquées suivant la parité du nombre n d'atomes de carbone. Les maximums ont lieu quand n est impair pour FpC+n (p = 1-3) et quand n est pair dans les autres cas (p = 4 ; ions négatifs). On interprète les alternances des ions FpC+n et F PC-n (p = 1, 2) avec un calcul CNDO dans le modèle de la chaîne linéaire Cn analogue à celui de Pitzer et Clementi. On trouve alors que les stabilités relatives des agrégats linéaires sont les plus fortes pour les ions FC+2+k+ 1, F2C+2k+1,FC-2k et F2C-2k, ce qui est en très bon accord avec la « règle de correspondance » entre les émissions des différents ions et leurs stabilités relatives. En outre, dans le cas des chaines F 2Cn, le calcul montre que ce sont les isomères dissymétriques qui donnent le meilleur accord avec les résultats expérimentaux

Person W.b. - One of the best experts on this subject based on the ideXlab platform.

  • CNDO Calculation Of Dipole Moment Derivatives And Infrared Intensities Of Formaldehyde
    2015
    Co-Authors: Bruns R.e., Person W.b.
    Abstract:

    The complete neglect of differential overlap (CNDO) approximate wavefunctions for formaldehyde have been applied to the Calculation of the derivatives of the dipole moment with respect to the symmetry coordinates (∂p/∂Sj). Agreement between the calculated derivatives and the experimental values given by Hisatsune and Eggers for the A1 symmetry species is exceptionally good, permitting an interpretation of the experimental results in terms of electronic distributions in the molecule. The agreement for the B1 and B2 symmetry species is also very good except for the asymmetric in-plane CH bend. However, the theory successfully predicts that charge reorientation for this motion is quite different from that which occurs in the out-of-plane CH bend, so that these motions are represented by CH bond moments of opposite polarity. An analysis is given of the results in terms of derivatives with respect to internal coordinates (∂p/∂rk). Comparison of ∂p/∂rCS values from a series of X2CO molecules (and also with ∂p/∂rcs for X2CS molecules) reveals an interesting trend. An analysis of the various contributions to the calculated ∂p/∂rk values is presented, with an explanation of the calculated results for the out-of-plane bending coordinate ∂p/∂γ.5862585259

Bruns R.e. - One of the best experts on this subject based on the ideXlab platform.

  • CNDO Calculation Of Dipole Moment Derivatives And Infrared Intensities Of Formaldehyde
    2015
    Co-Authors: Bruns R.e., Person W.b.
    Abstract:

    The complete neglect of differential overlap (CNDO) approximate wavefunctions for formaldehyde have been applied to the Calculation of the derivatives of the dipole moment with respect to the symmetry coordinates (∂p/∂Sj). Agreement between the calculated derivatives and the experimental values given by Hisatsune and Eggers for the A1 symmetry species is exceptionally good, permitting an interpretation of the experimental results in terms of electronic distributions in the molecule. The agreement for the B1 and B2 symmetry species is also very good except for the asymmetric in-plane CH bend. However, the theory successfully predicts that charge reorientation for this motion is quite different from that which occurs in the out-of-plane CH bend, so that these motions are represented by CH bond moments of opposite polarity. An analysis is given of the results in terms of derivatives with respect to internal coordinates (∂p/∂rk). Comparison of ∂p/∂rCS values from a series of X2CO molecules (and also with ∂p/∂rcs for X2CS molecules) reveals an interesting trend. An analysis of the various contributions to the calculated ∂p/∂rk values is presented, with an explanation of the calculated results for the out-of-plane bending coordinate ∂p/∂γ.5862585259