Rovibrational averaging of molecular magnetic properties of CH3F, CH2F2, and CHF3
Titel:
Rovibrational averaging of molecular magnetic properties of CH3F, CH2F2, and CHF3
Auteur:
Jameson, Cynthia J. Osten, H. Jorg
Verschenen in:
Molecular physics
Paginering:
Jaargang 56 (1985) nr. 5 pagina's 1083-1095
Jaar:
1985-12-10
Inhoud:
The mean bond displacements in the series of molecules CH3F, CH2F2, CHF3 have been calculated using the available harmonic force fields augmented by cubic terms in the stretching and non-bonded interactions, ignoring cubic terms in the bond angle deformation. With these dynamic factors we interpret the previously reported temperature dependence of 19F shielding in the zero-pressure limit as well as the 13C- and 2H-induced 19F isotope shifts in these molecules. We obtain values for the shielding derivatives (∂σF/∂ ΔrCF)e = -338, -725, and -1274 for CH3F, CH2F2, and CHF3 respectively. These shielding derivatives are shown to correlate linearly with n in CHnF4-n, and with the shielding tensor components parallel to the CF bond and perpendicular to the CF bond in the FCF plane. Together with the halomethanes CF3X, CF2Cl2, and CFCl3, they show a non-linear correlation with the absolute shielding and a nearly linear one with 1J(CF). From the D-induced 19F isotope shift in CHF3 we obtain an estimate (∂σF〉6 ΔrCH)e = -84 ppm Å-1. We also estimate (∂σF/∂ ΔrCF)e ≤ -1520 and -1400 ppm Å-1 CHFCl2 and CHF2Cl respectively. The errors associated with the empirical values of shielding derivatives are discussed.
Tijdschrift beschrijving