Vibrational excitation of diatomic molecular ions in strong-field ionization of diatomic molecules

A model based on the strong-field and Born-Oppenheimer approximations qualitatively describes the distribution over vibrational states formed in a diatomic molecular ion following ionization of the neutral molecule by intense laser pulses. Good agreement is found with a recent experiment [X. Urbain et al., Phys. Rev. Lett. 92, 163004 (2004)]. In particular, the observed deviation from a Franck-Condon-like distribution is reproduced. Additionally, we demonstrate control of the vibrational distribution by a variation of the peak intensity or a change of frequency of the laser pulse.Comment: 4 pages, 4 figure

Magnetometry with entangled atomic samples

We present a theory for the estimation of a scalar or a vector magnetic field by its influence on an ensemble of trapped spin polarized atoms. The atoms interact off-resonantly with a continuous laser field, and the measurement of the polarization rotation of the probe light, induced by the dispersive atom-light coupling, leads to spin-squeezing of the atomic sample which enables an estimate of the magnetic field which is more precise than that expected from standard counting statistics. For polarized light and polarized atoms, a description of the non-classical components of the collective spin angular momentum for the atoms and the collective Stokes vectors of the light-field in terms of effective gaussian position and momentum variables is practically exact. The gaussian formalism describes the dynamics of the system very effectively and accounts explicitly for the back-action on the atoms due to measurement and for the estimate of the magnetic field. Multi-component magnetic fields are estimated by the measurement of suitably chosen atomic observables and precision and efficiency is gained by dividing the atomic gas in two or more samples which are entangled by the dispersive atom-light interaction.Comment: 8 pages, 11 figure

Molecular orbitals and strong-field approximation

V.I. Usachenko and S.-I. Chu [Phys. Rev. A {\bf 71}, 063410 (2005)] discuss the molecular strong-field approximation in the velocity gauge formulation and indicate that some of our earlier velocity gauge calculations are inaccurate. Here we comment on the results of Usachenko and Chu. First, we show that the molecular orbitals used by Usachenko and Chu do not have the correct symmetry, and second, that it is an oversimplification to describe the molecular orbitals in terms of just a single linear combination of two atomic orbitals. Finally, some values for the generalized Bessel function are given for comparison.Comment: 4 pages, 3 figure

Control and femtosecond time-resolved imaging of torsion in a chiral molecule

We study how the combination of long and short laser pulses, can be used to induce torsion in an axially chiral biphenyl derivative (3,5-difluoro-3',5'-dibromo-4'-cyanobiphenyl). A long, with respect to the molecular rotational periods, elliptically polarized laser pulse produces 3D alignment of the molecules, and a linearly polarized short pulse initiates torsion about the stereogenic axis. The torsional motion is monitored in real-time by measuring the dihedral angle using femtosecond time-resolved Coulomb explosion imaging. Within the first 4 picoseconds, torsion occurs with a period of 1.25 picoseconds and an amplitude of 3 degrees in excellent agreement with theoretical calculations. At larger times the quantum states of the molecules describing the torsional motion dephase and an almost isotropic distribution of the dihedral angle is measured. We demonstrate an original application of covariance analysis of two-dimensional ion images to reveal strong correlations between specific ejected ionic fragments from Coulomb explosion. This technique strengthens our interpretation of the experimental data.Comment: 11 pages, 9 figure

Subtle Size Effects in C-H Activation Reactions of Lanthanum and Praseodymium Tetramethylaluminates by Neutral Trinitrogen Bases

Bojer D, Neumann B, Stammler H-G, Mitzel NW. Subtle Size Effects in C-H Activation Reactions of Lanthanum and Praseodymium Tetramethylaluminates by Neutral Trinitrogen Bases. European Journal of Inorganic Chemistry. 2011;(25):3791-3796.The reaction of Pr(AlMe(4))(3) with 1,3,5-trimethyl-1,3,5-triazacyclohexane (TMTAC) leads to the formation of two isomeric products by C-H activation of the AlMe(4)(-) ligands: [(eta(3)-TMTAC)Pr{eta(4)-(Me(3)AlCH(2)AlMe(2)CH(2)AlMe(3))}] (1), containing a linear tris(aluminate) trianion, and [(eta(3)-TMTAC)Pr(eta(4)-{CH(AlMe(3))(3)})] (2), containing a branched tris(aluminate) trianion. The analogous reaction with the more bulkily substituted 1,3,5-tri-tert-butyl-1,3,5-triazacyclohexane (TtBuTAC) leads selectively to [(eta(3)-TtBuTAC)Pr{mu(4)-(Me(3)AlCH(2)AlMe(2)CH(2)AlMe(3))}] (3). The reaction of La(AlMe(4))(3) with TtBuTAC affords [(eta(3)-TtBuTAC)La{eta(4)-(Me(3)AlCH(2)AlMe(2)CH(2)AlMe(3))}] (4). All compounds were characterised by elemental analysis and crystal-structure determination. Isomers 1 and 2 could not be separated and form a cocrystalline product with a 1/2 ratio of 1:2 with two slightly different structures of 2 (2a and 2b). In compounds 2, 3 and 4 the tris(aluminate) ligand [Me(3)AlCH(2)AlMe(2)CH(2)AlMe(3)](3-) is bonded to the lanthanide ions in an.4-mode through two CH(2) units and two terminal Me groups

Substituent Size Effects in Lewis Base Induced Reductions in Organolanthanide Chemistry

Bojer D, Neumann B, Stammler H-G, Mitzel NW. Substituent Size Effects in Lewis Base Induced Reductions in Organolanthanide Chemistry. Chemistry. 2011;17(22):6239-6247.The reaction of the tripodal 1,3,5-trialkyl-1,3,5-triazacyclohexanes (L= cyclo-[N(R) CH2](3), R= Et, iPr, tBu), with [Sm(AlMe4)(3)] resulted in the formation of divalent samarium complexes of the constitution [{LnSm(AlMe4)(2)}(m)] (n, m= 1,2) under ethane extrusion. These compounds were characterised by single-crystal X-ray diffraction and elemental analyses. Simultaneous occurrence of Lewis base induced reduction and C-H-activation reactions is observed. The ratio of products depends on the bulkiness of the N-alkyl substituent R. The reaction of [Sm(AlMe4)(3)] with 1,3,5-triisopropyl-1,3,5-triazacyclohexane (TiPTAC) in benzene afforded the inversion-symmetric dimer [{(TiPTAC)(eta(3)-AlMe4) Sm}(2)(mu(2)-AlMe4)(2)], whereas in toluene the pseudo-samarocene [(TiPTAC)(2)Sm(eta(1)-AlMe4)(2)] was obtained. The trisaluminate [(TiPTAC)-Sm{(mu 2-Me)(Me2Al)}(2)(mu(3)-CH2)(2)AlMe2)] was found to be the C-H-activation product. In the case of the particular bulky 1,3,5-tri-tert-butyl-1,3,5-triazacy clohexane (TtBuTAC), the reaction led to the formation of the dimeric [{(TtBuTAC)(eta(3)-AlMe4) Sm}(2)(mu(2)-AlMe4)(2)] even in toluene in comparably high yields. The decrease of the steric demand to ethyl groups in 1,3,5-triethyl- 1,3,5-triazacyclohexane (TETAC) afforded the samarocene-like [(TETAC)(2)Sm(eta(1)-AlMe4)(2)] in lower yields. The resulting divalent samarium compounds are found to be stable with respect to reagents like dinitrogen, conjugated olefins and polycyclic aromatic systems

Lewis Base Induced Reductions in Organolanthanide Chemistry

Bojer D, Venugopal A, Neumann B, Stammler H-G, Mitzel NW. Lewis Base Induced Reductions in Organolanthanide Chemistry. ANGEWANDTE CHEMIE-INTERNATIONAL EDITION. 2010;49(14):2611-2614