The control of electron distribution excited in a metal through optical phase of the excitation light is demonstrated. Two-photon photoemission from the Cu(111) surface is excited either by a pair of ϳ15 fs laser pulses with a mutual delay fixed to an accuracy of 60.025 fs, or by a single, frequency-chirped pulse. As a consequence of optical coherence in the two-photon excitation process, the photoemission spectra do not only depend on the frequency, as in conventional spectroscopy, but also on the phase of the excitation light. This may be a general phenomenon in multiphoton ionization.[S0031-9007(97)04735-2] PACS numbers: 73.50. Gr, 78.40.Kc, The reflection of light and flow of current in response to external, time-varying fields are defining electronic properties of metals. An electromagnetic wave with a frequency v , v p (v p is the plasma frequency) is attenuated exponentially at the metal-vacuum interface due to the dynamical response of electrons. The field creates a microscopic polarization at the surface, which can decay by reemission of the field (reflection), or by absorption of a photon (e-h creation). According to the Drude theory, the reflection and absorption of light by a free-electron metal are described, respectively, by the real and imaginary parts of the dielectric constant,´͑v͒ 1 2 v 2 p ͞v͑v 1 i͞t 0 ͒, where t 0 is the optical relaxation time [1,2]. The freecarrier absorption occurs as a second-order process, where a carrier absorbs a photon and simultaneously scatters with a phonon or impurity to conserve momentum. Elastic scattering destroys the phase relation between the excitation created in the sample and the external field. Thus, t 0 is a phenomenological dephasing time. Analysis of freecarrier absorption in noble metals shows that for visible light vt 0 . 1: For example, for Cu at 400 nm (3.1 eV), t 0 is ϳ3.5 fs [2], while an optical cycle is 1.33 fs. Thus, the scattering processes described by t 0 do not present a fundamental limit for controlling quantum dynamical response of electrons in metals by means of the optical phase.Coherent control of quantum dynamics is a rapidly developing field of physical sciences [3]. Demonstration of control of quantum dynamics in atoms [4], molecules [5,6], molecular crystals [7], and semiconductors [8] has been achieved with phase-engineered light pulse sequences and chirped pulse excitation [3]. Interference between oneand two-photon excitation has been used for control of electrical currents in semiconductors [9] and the direction of photoemission from a surface [10]. Optical control of electron dynamics in metals and at metallic interfaces also is of great interest in a variety of fields including solid state physics, surface science, and for applications in optoelectronics. However, the dephasing time implied by t 0 , which is less than the currently available laser pulse widths, seems to impose severe limits for demonstration and application of coherent control in metals. Nevertheless, development of ultrafast interferometric techniques for st...

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The crystal and molecular structures of dichlorobis(2-pyridinethiolato)tin(IV) have been determined by X-ray analysis. The crystal belongs to the triclinic system: a=8.340(8), b=12.456(7), c=7.178(3) Å, α=86.46(4), β=111.06(5), γ=99.18(6)°, space group P\bar1 with Z=2. The structure was determined by the heavy atom method and refined by the block-diagonal least-squares method (R=0.058). The complex is a distorted octahedral complex in which 2-pyridinethiolato ligands act as bidentate ligands, two four-membered (Sn, S, C, and N) chelate rings being present. Two Sn–Cl bonds are cis, two Sn–N bonds are cis, and two Sn–S bonds are trans configuration.

The reaction of di-2-pyridyl disulfide with tin(II) halides was found to give dihalogenobis(2-pyridinethiolato)-tin(IV). The oxidative addition reaction was successfully extended to the preparation of other dihalogenodi-thiolatotin(IV) complexes. Dichlorobis(2-pyridinethiolato)tin(IV) was also prepared by the reaction of 2(1H)-pyridinethione with tin(IV) chloride and proposed to be a monomeric, octahedral complex with a four-membered (Sn, S, C, and N) chelate ring from its molecular weight and IR spectral data. Dichlorobis(2-quinolinethiolato)tin(IV) could be isolated similarly as a stable complex. However, attempts to isolate the dichlorodithiolatotin(IV) in which an intramolecular chelation seems hardly possible were unsuccessful. The great stability of bis(2-pyridinethiolato)- and bis(2-quinolinethiolato)-dihalogenotin(IV) could be ascribed to the intramolecular four-membered chelate ring formation for the six-coordination of tin atom.