Michael Philpott - Academia.edu (original) (raw)

Papers by Michael Philpott

Astrobiology Science Conference 2010: Evolution and Life: Surviving Catastrophes and Extremes on Earth and Beyond, Apr 1, 2010

ABSTRACT

Langmuir, Jul 1, 1993

Itl lII 11111 i lI Il l .Iii R&T Code N o _4-92(_-0I, 73

ChemInform, Jun 12, 1990

ChemInform Abstract From a study of three IR active vibrational modes of bisulfate ions adsorbed ... more ChemInform Abstract From a study of three IR active vibrational modes of bisulfate ions adsorbed on Pt from 0.5 M sodium sulfate solution as a function of the electrode potential and the pH, it is concluded that the HSO3-ions adsorb via an oxygen atom of the SO3 unit with the axis passing through the S-(OH) bond at 72 rc from the surface normal in the double layer region. In the oxide region (the surface is oxygen covered) the bisulfate ions are H-bonded to the electrode surface, with the H-bond inclined at a significant angle (60 rc) with respect to the surface.

Journal of Chemical Physics, 1999

Polarized reflection spectra off the (010) face of the first singlet transition of crystalline te... more Polarized reflection spectra off the (010) face of the first singlet transition of crystalline tetracyanoquinodimethane (TCNQ) have been measured at room and liquid helium temperatures. The spectrum consists of a massive block of high reflectivity, corresponding to a stop band 1.4 eV wide, with well defined edges at 2.8 and 4.2 eV. The reflectivity of the long wavelength edge undergoes a large increase upon cooling, and vibrational structure appears between 2.8 and 3.1 eV due to freezing out of powerful polariton scatterers, the intramolecular vibrations. All structure is assoicated with volume polaritons since it is not shifted when the crystal is coated with a layer of frozen gas. The complex dielectric function, calculated by a Kramers–Kronig transformation, shows two regions where the real part ε1 is negative. The spectra provide a test of the basic notions of strong vibronic coupling in molecular crystals. Polariton scattering by lattice phonons is weak, whereas scattering by intramolecular modes is much stronger.

Proceedings of the Royal Society of London, Mar 15, 1966

The electronic states of mixed molecular crystals Calculations have been made of the exciton band... more The electronic states of mixed molecular crystals Calculations have been made of the exciton band structure of the naphthalene crystal in a periodic volume of 10x10x10 unit cells. Levels belonging to special values of wave vector are reported for the crystal structure at room temperature and at 95 °K. It is found that the ac polarized spectrally active level lies at the bottom of the exciton band, in agreement with experiment. The pure crystal levels are used in a calculation of the properties of dilute mixed crystals of naphthalene~& 8 in various deuterated naphthalene host crystals. Then the variation of optical properties with concentration is treated, the guests being assumed to form superlattices within the host structure. The dilute crystal results, and those for variation with concentration, agree satisfactorily with experiment.

Proceedings of the Royal Society of London, Jul 26, 1966

A theory of energy levels is given for rigid lattice mixed crystals in which the impurity differs... more A theory of energy levels is given for rigid lattice mixed crystals in which the impurity differs from the host in its intermolecular coupling properties as well as in excitation energy. The influence of secondary trapping sites, induced by the impurity in its neighbour host molecules, is considered. The effects of a vacancy, of an isotopically distinguished impurity, and of a deep trap are treated as special cases. While the band structure is sensitive in details to differences between host–guest and host–host resonance coupling its general features are unaffected except that for a range of values of coupling parameters and trap depths two levels may split away from the band instead of one. The secondary traps cause additional levels to split away from the band and are probably important in the process in which delocalized excitation in the host crystal becomes localized in the impurity, as in fluorescence quenching. Typical results of calculations based on the theory are given for mixed crystals with naphthalene as host.

The Journal of Chemical Physics, 1969

In this paper we consider the energy levels of dilute mixed crystals in the weak vibronic couplin... more In this paper we consider the energy levels of dilute mixed crystals in the weak vibronic coupling limit using the one-particle Green's-function method. The perturbation Hamiltonian is treated explicitly with reference to impurity molecules differing from the host molecules by isotopic substitution. The general equations derived for the energy levels, for excitation amplitudes, and for the optical properties of the mixed crystal are expressed in terms of the weighted density-of-states function of the pure crystal. This treatment emphasizes the relation between the density of exciton states in the pure crystal and the optical properties of mixed crystals. The nature of bound and virtual impurity states are considered, and new experiments using the impurity-induced electronic-absorption method are suggested.

It is shown that a better understanding of the geometry of adsorbed bisulfate species on the surf... more It is shown that a better understanding of the geometry of adsorbed bisulfate species on the surface is gained by simultaneously monitoring more than one vibrational mode of the molecule. We propose that in the double laver region the bisulfate ions are adsorbed via an oxygen atom of its S03 unit with the Pt-O-S linkage along the surface normal. In the oxide region the bisulfate ions are adsorbed on the oxygen covered surface of the platinum electrode via the hydrogen atom by hydrogen bonding with the hydrogen bond showing a significant tilt (approximately 60").

ChemInform, Jun 7, 1988

ChemInform Abstract The in-situ IR spectroscopic results obtained for a polycrystalline Pt electr... more ChemInform Abstract The in-situ IR spectroscopic results obtained for a polycrystalline Pt electrode in 0.05 M H2SO4 clearly show the coadsorption of HSO4-and SO42-. The different nature of the potential dependence of the HSO4 band and the SO42-band is discussed.

Journal of Photochemistry and Photobiology, 1976

Acs Symposium Series, Feb 28, 1997

ABSTRACT

Chemischer Informationsdienst, May 19, 1981

The Journal of Physical Chemistry, Sep 1, 1991

Pages 7411 and 7412. Figures 4 and 6 were inadvertently switched. The figure captions are correct... more Pages 7411 and 7412. Figures 4 and 6 were inadvertently switched. The figure captions are correct, but the figures themselves should be exchanged.

The Journal of Physical Chemistry, Sep 1, 1981

and isomeric nitrocresols are found as products in addition to the expected benzaldehyde and cres... more and isomeric nitrocresols are found as products in addition to the expected benzaldehyde and cresols. The appearance of 3-nitrotoluene is readily accounted for by the elevated (=1 ppm and greater) concentrations of NOz and high conversions used in the experiments. That the 2 and 4 isomers of nitrotoluene are observed is perplexing, because we have shown that OH attack meta to the methyl group (the reaction that would lead to the 2-and 4-nitrotoluenes) is of minor importance. Because ionic nitrations typically give predominately 2-and 4-substitution, and because we find27 NO, to be a powerful nitrating agent in condensing our reaction mixtures, we suggest that the observance of 2and 4-nitrotoluenes in smog-chamber studies is indicative of heterogeneous reactions that occur in the aerosol phase or during sampling of the products. Phenolic compounds are especially susceptible to heterogeneous nitration, and the origin of nitrophenols in smog-chamber experiments must be interpreted with extreme caution. Acknowledgment. We acknowledge Bosco Y. Lan for his technical assistance and the support of the Environmental Protection Agency under Research Grants R-803846 and R-806093.

Chemischer Informationsdienst, Aug 12, 1980

Journal of Electron Spectroscopy and Related Phenomena, 1983

The time development of surface enhanced Raman scattering from silver electrodes immersed in chlo... more The time development of surface enhanced Raman scattering from silver electrodes immersed in chloride and thiocyanate electrolytes has been measured during and after oxidation-reduction cycles of the linear scan and double step type. Raman spectra were recorded in times as short as 0.1 s, using a spectrograph equipped with an optical multichannel detector and analyzer. Correlations were found between Raman spectra and the current-potential-time curves. In mixed electrolytes the displacement of one anion by a more strongly adsorbing anion was observed. In addition, unexpectedly large effects of laser irradiation and hydrogen evolution prior to the oxidation-reduction cycle have been observed in the intensity of SERS bands after thecycle. These last two effects are attributed to the formation of peculiar surface morphologies.

Jerusalem Symposia on Quantum Chemistry and Biochemistry, 1984

Approved for public release; distribution unlimited. D II SELEC JUL 2 7 1984 17. DISTRIBUTION ST.... more Approved for public release; distribution unlimited. D II SELEC JUL 2 7 1984 17. DISTRIBUTION ST. lENT (of abetrct entered In Block 20, If different from Report) Approved for public release; distribution unlimited. B IS. SUPPLEMENTARY rES SPrepared for publication in Proceedings of the 17th Jerusalem Symposium 0_1 in Quantum Chemistry abd Biochemistry, to be published by D. Reidel Pub. Co. C-D L.J 19. KEY WORDS (Continue on reverse side it neceeery and identify by block number) Surface enhanced, Infrared Raman, Spectroscopy Electrode, Silver Electrolytes t , ABSTRACT (Continue on reverse side if necessiry and Identify by block number) The use of Raman and infrared spectroscopy to obtain the vibrational spectra of molecules and ions adsorbed at the metal electrode-aqueous electrolyte interface are described. To obtain Raman spectra, we use surface polaritons and roughness to enhanced spectral intensities. In the infrared, we use Fourier transform and modulated reflection-absorption techniques. Raman results for fatty acids, chloride, and thiocyanate on silver electrodes are presented, together with a combined Raman and infrared study of cyanide adsorbed on silver.\ DD ,jAN72 1473 SECURITY CLASSIFICATION OF THIS PAGE (When Dete Entered) 84 07 25 009 OFFICE OF NAVAL RESEARCH Contract ONR-NO0014-82-C-0583 NR-359-824 Raman and Infrared Spectroscopy of Molecules Adsorbed on Metal Electrodes

Annual Review of Physical Chemistry, Oct 1, 1980

Page 1. Ann. Rev. Phys. Chern. 1980. 31:97-129 Copyright © 1980 by Annual Reviews Inc. All rights... more Page 1. Ann. Rev. Phys. Chern. 1980. 31:97-129 Copyright © 1980 by Annual Reviews Inc. All rights reserved OPTICAL REFLECTION SPECTROSCOPY OF ORGANIC SOLIDS Michael R. Philpott IBM Research Laboratory, San Jose, California 95193 INTRODUCTION +2702 ...

Chemischer Informationsdienst, Jul 29, 1980

Astrobiology Science Conference 2010: Evolution and Life: Surviving Catastrophes and Extremes on Earth and Beyond, Apr 1, 2010

ABSTRACT

Langmuir, Jul 1, 1993

Itl lII 11111 i lI Il l .Iii R&T Code N o _4-92(_-0I, 73

ChemInform, Jun 12, 1990

ChemInform Abstract From a study of three IR active vibrational modes of bisulfate ions adsorbed ... more ChemInform Abstract From a study of three IR active vibrational modes of bisulfate ions adsorbed on Pt from 0.5 M sodium sulfate solution as a function of the electrode potential and the pH, it is concluded that the HSO3-ions adsorb via an oxygen atom of the SO3 unit with the axis passing through the S-(OH) bond at 72 rc from the surface normal in the double layer region. In the oxide region (the surface is oxygen covered) the bisulfate ions are H-bonded to the electrode surface, with the H-bond inclined at a significant angle (60 rc) with respect to the surface.

Journal of Chemical Physics, 1999

Polarized reflection spectra off the (010) face of the first singlet transition of crystalline te... more Polarized reflection spectra off the (010) face of the first singlet transition of crystalline tetracyanoquinodimethane (TCNQ) have been measured at room and liquid helium temperatures. The spectrum consists of a massive block of high reflectivity, corresponding to a stop band 1.4 eV wide, with well defined edges at 2.8 and 4.2 eV. The reflectivity of the long wavelength edge undergoes a large increase upon cooling, and vibrational structure appears between 2.8 and 3.1 eV due to freezing out of powerful polariton scatterers, the intramolecular vibrations. All structure is assoicated with volume polaritons since it is not shifted when the crystal is coated with a layer of frozen gas. The complex dielectric function, calculated by a Kramers–Kronig transformation, shows two regions where the real part ε1 is negative. The spectra provide a test of the basic notions of strong vibronic coupling in molecular crystals. Polariton scattering by lattice phonons is weak, whereas scattering by intramolecular modes is much stronger.

Proceedings of the Royal Society of London, Mar 15, 1966

The electronic states of mixed molecular crystals Calculations have been made of the exciton band... more The electronic states of mixed molecular crystals Calculations have been made of the exciton band structure of the naphthalene crystal in a periodic volume of 10x10x10 unit cells. Levels belonging to special values of wave vector are reported for the crystal structure at room temperature and at 95 °K. It is found that the ac polarized spectrally active level lies at the bottom of the exciton band, in agreement with experiment. The pure crystal levels are used in a calculation of the properties of dilute mixed crystals of naphthalene~& 8 in various deuterated naphthalene host crystals. Then the variation of optical properties with concentration is treated, the guests being assumed to form superlattices within the host structure. The dilute crystal results, and those for variation with concentration, agree satisfactorily with experiment.

Proceedings of the Royal Society of London, Jul 26, 1966

A theory of energy levels is given for rigid lattice mixed crystals in which the impurity differs... more A theory of energy levels is given for rigid lattice mixed crystals in which the impurity differs from the host in its intermolecular coupling properties as well as in excitation energy. The influence of secondary trapping sites, induced by the impurity in its neighbour host molecules, is considered. The effects of a vacancy, of an isotopically distinguished impurity, and of a deep trap are treated as special cases. While the band structure is sensitive in details to differences between host–guest and host–host resonance coupling its general features are unaffected except that for a range of values of coupling parameters and trap depths two levels may split away from the band instead of one. The secondary traps cause additional levels to split away from the band and are probably important in the process in which delocalized excitation in the host crystal becomes localized in the impurity, as in fluorescence quenching. Typical results of calculations based on the theory are given for mixed crystals with naphthalene as host.

The Journal of Chemical Physics, 1969

In this paper we consider the energy levels of dilute mixed crystals in the weak vibronic couplin... more In this paper we consider the energy levels of dilute mixed crystals in the weak vibronic coupling limit using the one-particle Green's-function method. The perturbation Hamiltonian is treated explicitly with reference to impurity molecules differing from the host molecules by isotopic substitution. The general equations derived for the energy levels, for excitation amplitudes, and for the optical properties of the mixed crystal are expressed in terms of the weighted density-of-states function of the pure crystal. This treatment emphasizes the relation between the density of exciton states in the pure crystal and the optical properties of mixed crystals. The nature of bound and virtual impurity states are considered, and new experiments using the impurity-induced electronic-absorption method are suggested.

It is shown that a better understanding of the geometry of adsorbed bisulfate species on the surf... more It is shown that a better understanding of the geometry of adsorbed bisulfate species on the surface is gained by simultaneously monitoring more than one vibrational mode of the molecule. We propose that in the double laver region the bisulfate ions are adsorbed via an oxygen atom of its S03 unit with the Pt-O-S linkage along the surface normal. In the oxide region the bisulfate ions are adsorbed on the oxygen covered surface of the platinum electrode via the hydrogen atom by hydrogen bonding with the hydrogen bond showing a significant tilt (approximately 60").

ChemInform, Jun 7, 1988

ChemInform Abstract The in-situ IR spectroscopic results obtained for a polycrystalline Pt electr... more ChemInform Abstract The in-situ IR spectroscopic results obtained for a polycrystalline Pt electrode in 0.05 M H2SO4 clearly show the coadsorption of HSO4-and SO42-. The different nature of the potential dependence of the HSO4 band and the SO42-band is discussed.

Journal of Photochemistry and Photobiology, 1976

Acs Symposium Series, Feb 28, 1997

ABSTRACT

Chemischer Informationsdienst, May 19, 1981

The Journal of Physical Chemistry, Sep 1, 1991

Pages 7411 and 7412. Figures 4 and 6 were inadvertently switched. The figure captions are correct... more Pages 7411 and 7412. Figures 4 and 6 were inadvertently switched. The figure captions are correct, but the figures themselves should be exchanged.

The Journal of Physical Chemistry, Sep 1, 1981

and isomeric nitrocresols are found as products in addition to the expected benzaldehyde and cres... more and isomeric nitrocresols are found as products in addition to the expected benzaldehyde and cresols. The appearance of 3-nitrotoluene is readily accounted for by the elevated (=1 ppm and greater) concentrations of NOz and high conversions used in the experiments. That the 2 and 4 isomers of nitrotoluene are observed is perplexing, because we have shown that OH attack meta to the methyl group (the reaction that would lead to the 2-and 4-nitrotoluenes) is of minor importance. Because ionic nitrations typically give predominately 2-and 4-substitution, and because we find27 NO, to be a powerful nitrating agent in condensing our reaction mixtures, we suggest that the observance of 2and 4-nitrotoluenes in smog-chamber studies is indicative of heterogeneous reactions that occur in the aerosol phase or during sampling of the products. Phenolic compounds are especially susceptible to heterogeneous nitration, and the origin of nitrophenols in smog-chamber experiments must be interpreted with extreme caution. Acknowledgment. We acknowledge Bosco Y. Lan for his technical assistance and the support of the Environmental Protection Agency under Research Grants R-803846 and R-806093.

Chemischer Informationsdienst, Aug 12, 1980

Journal of Electron Spectroscopy and Related Phenomena, 1983

The time development of surface enhanced Raman scattering from silver electrodes immersed in chlo... more The time development of surface enhanced Raman scattering from silver electrodes immersed in chloride and thiocyanate electrolytes has been measured during and after oxidation-reduction cycles of the linear scan and double step type. Raman spectra were recorded in times as short as 0.1 s, using a spectrograph equipped with an optical multichannel detector and analyzer. Correlations were found between Raman spectra and the current-potential-time curves. In mixed electrolytes the displacement of one anion by a more strongly adsorbing anion was observed. In addition, unexpectedly large effects of laser irradiation and hydrogen evolution prior to the oxidation-reduction cycle have been observed in the intensity of SERS bands after thecycle. These last two effects are attributed to the formation of peculiar surface morphologies.

Jerusalem Symposia on Quantum Chemistry and Biochemistry, 1984

Approved for public release; distribution unlimited. D II SELEC JUL 2 7 1984 17. DISTRIBUTION ST.... more Approved for public release; distribution unlimited. D II SELEC JUL 2 7 1984 17. DISTRIBUTION ST. lENT (of abetrct entered In Block 20, If different from Report) Approved for public release; distribution unlimited. B IS. SUPPLEMENTARY rES SPrepared for publication in Proceedings of the 17th Jerusalem Symposium 0_1 in Quantum Chemistry abd Biochemistry, to be published by D. Reidel Pub. Co. C-D L.J 19. KEY WORDS (Continue on reverse side it neceeery and identify by block number) Surface enhanced, Infrared Raman, Spectroscopy Electrode, Silver Electrolytes t , ABSTRACT (Continue on reverse side if necessiry and Identify by block number) The use of Raman and infrared spectroscopy to obtain the vibrational spectra of molecules and ions adsorbed at the metal electrode-aqueous electrolyte interface are described. To obtain Raman spectra, we use surface polaritons and roughness to enhanced spectral intensities. In the infrared, we use Fourier transform and modulated reflection-absorption techniques. Raman results for fatty acids, chloride, and thiocyanate on silver electrodes are presented, together with a combined Raman and infrared study of cyanide adsorbed on silver.\ DD ,jAN72 1473 SECURITY CLASSIFICATION OF THIS PAGE (When Dete Entered) 84 07 25 009 OFFICE OF NAVAL RESEARCH Contract ONR-NO0014-82-C-0583 NR-359-824 Raman and Infrared Spectroscopy of Molecules Adsorbed on Metal Electrodes

Annual Review of Physical Chemistry, Oct 1, 1980

Page 1. Ann. Rev. Phys. Chern. 1980. 31:97-129 Copyright © 1980 by Annual Reviews Inc. All rights... more Page 1. Ann. Rev. Phys. Chern. 1980. 31:97-129 Copyright © 1980 by Annual Reviews Inc. All rights reserved OPTICAL REFLECTION SPECTROSCOPY OF ORGANIC SOLIDS Michael R. Philpott IBM Research Laboratory, San Jose, California 95193 INTRODUCTION +2702 ...

Chemischer Informationsdienst, Jul 29, 1980