Laser-induced splittings in the nuclear magnetic resonance spectra of the rare gases

Circularly polarized laser field causes a shift in the nuclear magnetic resonance (NMR) spectra of all substances. The shift is proportional to the intensity of the laser beam and yields oppositely signed values for left- and right-circularly polarized light, CPL -/+, respectively. Rapid switching -- in the NMR time scale -- between CPL+ and CPL- gives rise to a splitting of the NMR resonance lines. We present uncorrelated and correlated quadratic response calculations of the splitting per unit of beam intensity in the NMR spectra of $^{21}$Ne, $^{83}$Kr, and $^{129}$Xe. We study both the regions far away from and near to optical resonance and predict off-resonance shifts of the order 0.01, 0.1, and $1\times 10^{-6}$ Hz for $^{21}$Ne, $^{83}$Kr, and $^{129}$Xe, respectively, for a beam intensity of 10 W/cm$^2$. Enhancement by several orders of magnitude is predicted as the beam frequency approaches resonance. Only then can the effect on guest $^{129}$Xe atoms be potentially useful as a probe of the properties of the host material.Comment: 5 pages, 1 figur

Interplay of Aromaticity and Antiaromaticity in N-Doped Nanographenes

The aromaticity of three nonplanar, fully conjugated aza-nanographenes built around a pyrrolo[3,2-b]pyrrole core is assessed through the application of two different computational procedures—GIMIC and NICS. We examine the calculated magnetically induced current densities (GIMIC) and nucleus-independent chemical shifts (NICS). The structural differences between these three apparently similar molecules lead to significantly different aromatic properties. GIMIC analysis indicates that the peripheral diatropic ring current of 3.9 nA/T for the studied bowl-shaped diaza-nanographene is the strongest, followed by the double [6]helicene which lacks seven-membered rings, and is practically nonexistent for the double [5]helicene possessing seven-membered rings. The biggest difference however is that in the two not-fully-fused molecules, the central pyrrole rings possess a significant diatropic current of about 4.1 nA/T, whereas there is no such current in the diaza-nanographene. Moreover, the antiaromaticity of the seven-membered rings is increasing while moving from double [5]helicene to diaza-nanographene (from −2.4 to −6.0 nA/T). The induced currents derived from NICSπ,zz-XY-scan analysis for all of the studied systems are in qualitative agreement with the GIMIC results. Subtle differences may originate from σ-electron currents in GIMIC or inaccuracy of NICSπ,zz values due to the nonplanarity of the systems, but the general picture is similar.Peer reviewe

Research note: Scf calculations of the nmr shielding tensor for the ethylenic carbon atom in C3Cl4

Large differences have been reported in previous SCF calculations of the NMR shielding tensor of the ethylenic carbon atom in tetrachlorocyclopropene. Our calculations show that these differences are due to the use of different molecular geometries, not to differences in the methods applied to obtain gauge-invariance. © 1995 Taylor & Francis Ltd