Publications

    E. Mazur. 1988. “Doing Physics with Computers.” In Academic Computing, February: Pp. 18–21, 46-48. Publisher's VersionAbstract
    Are the days of watching analog meters, taking notes in thick lab books and plotting data points on graph paper gone forever? Is research in the physical sciences becoming so complex that one can no longer do research without computers? A superficial survey of the current research in physics might lead one to give an affirmative answer to these questions. It is therefore interesting to note that the award of this year's Nobel Prize in physics to Alex Mller and Georg Bednorz for their work on superconductivity was hailed as a victory for relatively simple, small-scale research. No computer was needed to show that their compound of copper, oxygen, lanthanum and barium becomes superconducting. It shows that one can still make major breakthroughs with very simple means-without computers. Computers excel at performing tedious routine tasks. Physics research on the other hand seldom entails routine work. This holds true in particular in theoretical physics: indeed, no computer has yet been able to develop a new theory. Yet one cannot deny that the presence of computers in physics research and education increases every day. Physics papers on results that have been obtained with the help of computers abound, and some fields of physics would not even exist without computers. As a physicist, I will try to analyze in this article the impact of computers on physics. I will start by analyzing the current situation using examples from my own laboratory.
    E. Mazur. 1988. “The interaction of intense picosecond infrared pulses with isolated molecules.” In Atomic and Molecular Processes with Short Intense Laser Pulses, edited by A. D. Bandrauk, Pp. 329–336. Plenum. Publisher's VersionAbstract
    In the Past decade there has been much interest in the dynamics of highly vibrationally excited and dissociating molecules. Selectivity at high levels of excitation may eventually lead to the realization of laser-controlled photochemistry, with broad applications in such diverse areas as laser- asisted chemical vapor deposition, isotope separation, and photosythesis. Polyatomic molecules in the ground electronic state can reach levels of excitation up to the dissociation threshold by absorbing a large number of photons from a resonant high-poewr infrared laser. Despite the selectivity of infrared excitation at low energy, however, at high excitation the excitation energy is no longer confined to one 'mode'. It has been shown experimentally that that for molecules excited close to or above the dissociation threshold equilibriation of energy occurs, in agreement with threoretical predictions. There is no agreement, however, as to the validity of theoretical models presuppose equipartitioning of energy in the region below the dissociation threshold. Recent spontaneous Raman spectroscopy experiments on infrared multiphoton excited molecules in our laboratory provide information on the intramolecular vibrational energy distributions of excess of energy can remain in the pumped mode up to levels of excitation close to the dissociation threshold. This paper provides a review of the results that were obtained in the past three years, part of which were published previously.
    J. Wang, K. Hsien Chen, and E. Mazur. 1987. “Highly nonthermal intramolecular energy distribution in isolated infrared multiphoton excited CF2Cl2 molecules.” In Laser Spectroscopy VIII, edited by S. Svanberg, Pp. 236–238. Springer-Verlag. Publisher's VersionAbstract
    When a polyatomic molecule with a strong vibrational absorption band is irradiated with an intense resonant infrared laser pulse it can absorb many (10 to 40) infrared photons. If some initial energy deposition is localizedpreferably in one vibrational mode or in a subset of modesit may become possible to induce mode-selective reactions by infrared multiphoton excitation. The intramolecular dynamics of infrared multiphoton excited molecules has been studied by a variety of spectroscopic techniques. One of these techniques is spontaneous Raman spectroscopy. In the past five years this technique has been successfully applied to monitor the vibrational energy in infrared multiphoton excited molecules. In this work we present experimental results of recent time-resolved spontaneous Raman experiments on collisionless infrared multiphoton excited CF2Cl2 molecules. The experiments show that the intramolecular energy distribution is highly nonthermal, and that a large part of the vibrational energy remains localized in the pump mode for a period of time long compared to the mean free time of the molecules.
    E. Mazur and D. S. Chung. 1987. “Light-scattering from the liquid-vapor interface.” Physica, 147A, Pp. 387–406. Publisher's VersionAbstract
    This paper presents light scattering spectra from the liquid-vapor interface of water and ethanol. Both quasi-elastic (Rayleigh) scattering and inelastic (Brillouin) scattering from fluctuations at the interface are observed. The spectra were obtained using a novel Fourier transform heterodyne technique that allows one to resolve the full Rayleigh-Brillouin triplet. Capillary waves travelling in opposite directions can therefore be separated, making the present technique suitable for studying nonequilibrium effects in interfaces.
    E. Mazur. 1987. “Fourier transform heterodyne spectroscopy: a simple novel technique with ultrahigh (150 mHz) resolution.” In Laser Spectroscopy VIII, edited by S. Svanberg, Pp. 390–392. Springer-Verlag. Publisher's VersionAbstract
    Light beating spectroscopy has been used from the early days of the laser to study light scattering. By detecting the beating signal between the scattered light and a 'local oscillator' field derived from the same laser, resolving powers of 10^14 have been achieved. The Fourier transform heterodyne spectroscopy presented here is simpler and more direct than the conventional heterodyne techniques using autocorrelators or spectrum analyzers.
    R. G. Cole, E. A. Mason, and E. Mazur. 1987. “Theory of thermomagnetic effects in the transition regime.” J. Chem. Phys., 87, Pp. 2236–2245. Publisher's VersionAbstract
    A simple model is presented that describes the complex behavior of the magnetic field dependence of the thermal conductivity of a polyatomic gas as a function of the Knudsen number. The model treats the solid surface as one component of a gas mixture, and a first-order Chapman-Enskog solution is adequate to account for the thermomagnetic effects in single gases. The results provide an interpolation scheme between the continuum and Knudsen regimes, in the form of scaling rules in which the Knudesen number appears in the coefficients and arguments of the functions that describe the limiting cases. Good agreement is obtained with the available experimental data, and leads to the conclusion that different surface accommodation coefficients are needed for the translational and internal energies of the gas molecules. This conclusion is consistent with analysis of independent field-free conductivity data, and with independent vibrating-surface measurements.
    K. Hsien Chen, J. Wang, and E. Mazur. 1987. “Nonthermal intramolecular vibrational energy distribution in infrared-multiphoton-excited CF2Cl2.” Phys. Rev. Lett., 59, Pp. 2728–2731. Publisher's VersionAbstract
    The intramolecular vibrational energy distribution of infrared multiphoton excited CF2Cl2 molecules is studied using time-resolved spontaneous Raman scattering. The time evolution of the signals from three vibrational modes is studied up to 600 ns after excitation and in the presence of N2 buffer gas. Following collisionless infrared multiphoton excitation a non-thermal distribution of vibrational energy is observed. The experimental result shows that equilibration of the intra-molecular vibrational energy distribution does not occur in this molecule up to at least 10,000 cm-1 of total internal vibrational energy. Note: also see Comment and Reply published separately.
    E. Mazur. 1986. “Computer-controlled Raman spectrometer for time-resolved measurements in low pressure gaseous sample.” Rev. Sci. Instrum., 57, Pp. 2507–2511. Publisher's VersionAbstract
    A spectrometer for measuring spontaneous Raman scattering in gaseous samples at pressures below 100 Pa (0.75 torr) with nanosecond time resolution is presented. The apparatus was developed for studying intramolecular vibrational energy distributions in infrared multiphoton excited molecules, and makes it possible to study the anti-Stokes Raman scattering from isolated molecules at pressures down to 14 Pa (110 mtorr). Because of the low level of the signals the measurements are completely computer-controlled. A detailed description of the apparatus, including the multichannel data-acquisition hardware and computer interface, is
    J. Wang, K. Hsien Chen, and E. Mazur. 1986. “Time-resolved spontaneous Raman spectroscopy of infrared-multiphoton-excited SF6.” Phys. Rev. A, 34, Pp. 3892–3901. Publisher's VersionAbstract
    Spontaneous Raman spectroscopy is used as a tool for studying the vibrational energy distribution of collisionless infrared multiphoton excited SF6. A collisionless increase in Stokes and anti-Stokes signals from the strong Raman-active n1-mode is observed after infrared multiphoton excitation by a high-power 500 ps CO2-laser pulse tuned to the infrared active n3-mode. Results are presented over a pressure range from 13 Pa (100 mtorr) to 270 Pa (2 torr). The pressure dependence clearly proves that the increase does not depend on collisions. The effects are studied as a function of time and of the infrared energy fluence, infrared wavelength and infrared pulse duration. The experimental data show that an intramolecular equilibrium of vibrational energy is established within the 20 ns time-resolution of the experimental setup. The multiphoton excitation shows a red shift and intensity broadening. A comparison with results from photoacoustic measurements is made.
    D. Korff, E. Mazur, C. Duzy, and A. Flusberg. 1986. “Raman conversion using crossed broadband pump beams and bisecting Stokes.” J. Opt. Soc. Am. B, 3, Pp. 1333–1337. Publisher's VersionAbstract
    The effects of stimulated Raman conversion under the conditions of crossed pump beams and a bisecting injected Stokes are examined. It is found that the beam quality of the emerging Stokes wave and the effective gain can be characterized by the following two parameters: the temporal coherence of the crossed pump beams and the angle between the pumps.
    E. Mazur, K. Hsien Chen, and J. Wang. 1986. “The interaction of infrared radiation with isolated molecules: intramolecular nonequilibrium.” In . Int. Conf. on Lasers '86. Publisher's VersionAbstract
    Anti-Stokes signals from various modes of isolated, infrared multiple photon excited molecules are measured to determine the intramolecular distribution of vibrational energy. This paper presents results for CF2HCl, CF2Cl 2, SF6 and 1,1-p;C2H 4F2. All but CF2HCl exhibit collisionless changes in Raman spectrum after infrared multiphoton excitation. This shows that the excitation modifies the population of these modes. Even though the symmetric SF 6 molecule reaches an intramolecular equilibrium within the 20 ns time resolution of the experiment, the other molecules exhibit a distinct nonequilibrium intramolecular distribution of vibrational excitation energy.
    H. Van Houten, E. Mazur, and J. J. M. Beenakker. 1985. “The temperature dependence of flow birefringence in gases and the scalar factor of angular momentum polarization in viscous flow.” Chem. Phys. Lett., 113, Pp. 135–139.Abstract
    Flow birefringence measurements have been performed for several linear molecules between 90 and 293 K. From a comparison with viscomagnetic effect data, information is obtained about the scalar factor of the angular momentum polarization present in viscous flow, of which only the tensorial factor had been determined. Experiments on hydrogen isotopes, for which only one rotational level is excited, confirm the assumption that the polarization does not depend on the translational energy.
    E. A. Mason and E. Mazur. 1985. “Theory of field effects on transport properties of polyatomic gases in the transition regime.” Physica, 130A, Pp. 437–464. Publisher's VersionAbstract
    A simple method is presented for describing the effects of external magnetic or electric fields on the transport properties of polyatomic gases over the entire range from the continuum to the Knudsen regime. Instead of treating bulk and boundary-layer effects separately, both molecular and surface scattering are included from the beginning in the collisional part of the Boltzmann equation, and the surface is treated as one component of a multicomponent mixture. A simple first-order solution of this problem is sufficient to account for the dependence of the transport coefficients on the Knudsen number in the presence of a field. Detailed results for the longitudinal and transverse viscomagnetic effects in a single gas are presented, and shown to be in good agreement with experimental data for CO and N2.
    E. Mazur, H. Van. Houten, and J. J. M. Beenakker. 1985. “A comparison of data on the viscomagnetic effect, flow birefringence and depolarized Rayleigh line broadening.” Physica, 130A, Pp. 505–522. Publisher's VersionAbstract
    A comparison of data on the viscomagnetic effect, flow birefringence and depolarized Rayleigh line broadening for various gases of linear molecules at temperatures between 90 and 293 K is carried out. From the combined results information is obtained on the scalar structure of the non-equilibrium angular momentum polarization produced in viscous flow.
    T. B. Simpson, E. Mazur, I. Burak, and N. Bloembergen. 1984. “Infrared multiphoton excitation of small molecules.” Israel J. Chem., 24, Pp. 179–186. Publisher's VersionAbstract
    The collisionless infrared multiphoton excitation of small molecules, OCS, SO2, NO2 and DN3 is discussed. Depite the small absorbance of IR photons by these molecules, evidence for the population of highly excited vibronic levels below the dissociation threshold is obtained. Multiphoton dissociation is observed, as well. The average number of photons absorbed and dissociation yields depend predominately on the laser intensity. High order multiphoton processes couple the ground vibrational level with the quasicontinuum of excited levels below and above the dissociation threshold.
    E. Mazur, H. J. M. Hijnen, L. J. F. Hermans, and J. J. M. Beenakker. 1984. “Experiments on the influence of a magnetic field on diffusion in N2-noble gas mixtures.” Physica, 123A, Pp. 412–427. Publisher's VersionAbstract
    Experimental results are presented for the magnetic field effect on diffusion in N2-noble gas mixtures at 300 K. The data show that the polarization produced by a concentration gradient is different from the one produced in a temperature gradient and that this difference is due to a different scalar part of the polarizations.
    E. Mazur and P. Mazur. 1984. “General expression for the matrix of saturated field effects.” Phys. Rev. A, 29, Pp. 991–993. Publisher's VersionAbstract
    A general expression for the change in transport coefficients of a dilute gas in the limit of an infinite external magnetic or electric field is derived without using a perturbation expansion of the collision operator. Previously derived properties of the saturated field effects are subsequently generalized and some implications are discussed.
    T. B. Simpson, E. Mazur, K. K. Lehmann, I. Burak, and N. Bloembergen. 1983. “The infrared multiphoton excitation and photochemistry of DN3.” J. Chem. Phys., 79, Pp. 3373–3381. Publisher's VersionAbstract
    Multiphoton excitation and dissociation of DN3 by short CO2 laser pulses is shown to be a collisionless process. The characteristic features of this multiphoton process are systematically studied. The average number of photons absorbed per DN3 molecule and the absolute dissociation yield show a strong dependence on the peak laser intensity. Resonantly enchanced coherent multiphoton excitation, rather than stepwise incoherent excitation, is suggested. The primary dissociation products of DN3 are ND[1delta] and N2. Formation of vibrationally excited ND[1delta] intermediates is suggested. The reactions of ND[1delta] with DN3 lead to chemiluminescent signals originating from the formation of electronically excited ND2[2A1] and ND[3II]. Formation of the ND[3II] intermediate is attributed to a reaction of ND[1delta] and vibrationally excited DN3 molecules: ND[1delta]+DN3-ND[3II]+ND[3-]+N2.
    E. Mazur, J. J. M. Beenakker, and I. Kuscer. 1983. “Kinetic theory of field effects in nonuniform molecular gases.” Physica, 121A, Pp. 430–456. Publisher's VersionAbstract
    Effects of magnetic and electric fields on transport phenomena in dilute polyatomic gases are reviewed within the framework of first order Enskog theory. The established technique of approximate operator inversion is used to give first order approximations of the transport coefficients. Instead of the customary expansion of polarizations into orthogonal polynomials a more general treatment is chosen here so as to accommodate recent experimental observations. The polarizations produced by macroscopic fluxes are assumed to be eigenfunctions of the collision operator within the subspace of functions anisotropic in angular momentum. The formalism is extended to mixtures in a way to let the final experssions assume the same form as for pure gases. The obtained transport coefficients obey several symmetry relations and inequalities. Additional inequalities are now also derived for the matrix describing the saturated field effects.

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