Papers by John C . Polanyi
International Journal: Canada's Journal of Global Policy Analysis, 1962
Atomic and Molecular Beams, 2001
The objective of the pioneers of molecular-beam chemistry [1] was, in the first place, to do chem... more The objective of the pioneers of molecular-beam chemistry [1] was, in the first place, to do chemistry under single-collision conditions, where all but the primary reactive events were eliminated. Their second aim was to localise the collision events in space, so that the speeds and angular distributions of the scattered species could be measured with respect to that localised region. Their third objective was to control the reagent attributes such as reagent energies and angles of approach (defined by electromagnetically aligning the molecule under attack).
The Journal of Chemical Physics, 1970
A previous investigation of the effect of barrier location on the reaction dynamics of reactions ... more A previous investigation of the effect of barrier location on the reaction dynamics of reactions A + BC → AB + C (Paper I) has been extended to the four-atom bimolecular reaction AB + CD → AC + BD. “Barrier location” is defined in terms of a 3d “diagnostic” potential-energy surface, namely the surface for reaction by way of rectangular coplanar configurations. Surface I had a barrier displaced by about 0.3 Å into the entry valley (or “approach coordinate”), and surface II had a barrier displaced by the same amount into the exit valley (or “retreat coordinate”). On both surfaces the classical barrier height was Ec = 34–35 kcal mol−1. A total of 22 batches of classical trajectories were run, across these two surfaces. The reacting molecules were free to move in three dimensions, i.e., reaction took place across the full 7d potential-energy hypersurface. The batches differed for the most part in the magnitude and distribution of the reagent energy. The reagent energy was restricted to ...
Chemical Physics, 1977
Abstract (i) Reagent vibrational energy is converted into product vibrational excitation with hig... more Abstract (i) Reagent vibrational energy is converted into product vibrational excitation with high efficiency in the thermoneutral reaction Cl + OH † → H
Applied Optics, 1971
The method of measured relaxation is described for the determination of initial vibrational energ... more The method of measured relaxation is described for the determination of initial vibrational energy distribution in the products of exothermic reaction. Hydrogen atoms coming from an orifice were diffused into flowing chlorine gas. Measurements were made of the resultant ir chemiluminescence at successive points along the line of flow. The concurrent processes of reaction, diffusion, flow, radiation, and deactivation were analyzed in some detail on a computer. A variety of relaxation models were used in an attempt to place limits on k(v'), the rate constant for reaction to form HCl in specified vibrational energy k(v') levels: H + C12 > HClv' + Cl. The set of k(v') obtained from this work is in satisfactory agreement TOP WINDOW 3-5 cm 2 cm MIDDLE WINDOW X ' 4 cm 2 cm BOTTOM WINDOW 6 cm ca. 17 cm
Journal of the American Chemical Society, 2021
Reaction dynamics examines molecular motions in reactive collisions. The aiming of reagents at on... more Reaction dynamics examines molecular motions in reactive collisions. The aiming of reagents at one another has been achieved at selected miss distances (impact parameters, b) by using the corrugations on crystalline surfaces as collimator. Prior experimental work and ab initio calculation showed single atoms aimed at chemisorbed molecules with b = 0 gave knock-on of atomic reaction products through a linear transition state. Here we report a study of b = 0 collision between directed CF2 and stationary chemisorbed CF3. Experiments and ab initio calculations again show linear reaction with a linear transition state, despite the additional degrees of freedom for CF2. The directed motion of CF2 is conserved through this linear transition state. Conservation of directionality is evidenced experimentally by the observation of a knock-on chain reaction along a line of chemisorbed CF3.
Bulletin of the Atomic Scientists, 1976
The Journal of Physical Chemistry C, 2019
We report the observation of electron-induced unidirectional planar molecular rotation of para-ch... more We report the observation of electron-induced unidirectional planar molecular rotation of para-chlorostyrene on Si(100), studied by scanning tunneling microscopy (STM) at room temperature and by ab initio theory. This bifunctional molecule is shown to be favorable to the electron-induced rotation since the phenyl group acts as a pivot and the vinyl as a lever arm. In the initial configuration, both phenyl and vinyl are attached to silicon dimers along the same row of the substrate. The first electron from the STM tip is observed to induce a lateral shift of the vinyl to “state 1” in which the vinyl is bound asymmetrically to one side of a silicon dimer. The second electron is found to give rise to a ∼60° rotation to “state 2”, a configuration in which the vinyl has swung around the phenyl to an adjacent dimer row. The impulsive two-state (I2S) model was employed to explain the conversion of the initial state to state 1 and the conversion of state 1 to state 2. These two successive impulses were computed b...
Advanced Series in Physical Chemistry, 1995
Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 1960
The technique described in part I has been used to obtain constants of interest in molecular spec... more The technique described in part I has been used to obtain constants of interest in molecular spectroscopy. The vibration-rotation interaction factor, F for HCl has been evaluated from the infra-red emission spectrum. The critical parameter in F is θ = M 0 / M 1 r e , where M 0 and M 1 are the first two coefficients in the electric dipole moment expansion about the equilibrium internuclear distance r e . A value of θ = + 1.12 ± 0.18 has been obtained. It is shown that for molecules with θ = +1 the total band intensity in emission is independent of the rotational distribution in the vibrational state from which the emission occurs. This has been made use of in evaluating radiative transition probabilities. For the HCl v (3-1) transition a value for | R 3 1 | 2 (= 1.60 x 10 -4 debye 2 ) was obtained for the first time. The same method yields a value of | R 2 1 | 2 / | R 2 0 | 2 = 204, in good agreement with an earlier estimate from absorption data.
Journal of the American Chemical Society, 2011
Adsorbates on metals, but not previously on semiconductors, have been observed to display long-ra... more Adsorbates on metals, but not previously on semiconductors, have been observed to display long-range repulsive interactions. On metals, due to efficient dissipation, the repulsions are weak, typically on the order of 5 meV at 10 Å. On the 7Â7 reconstruction of the Si(111) surface, charge transport through the surface has been demonstrated by others using charge injection by STM tips. Here we show that for both physisorbed brominated molecules, and for chemisorbed Br-atoms, induced chargetransfer in the Si(111)-7Â7 surface can lead to a strong repulsive interaction between adsorbates, calculated as 200 meV at 13.4 Å. This large repulsive interaction must be channeled through the surface since it causes widely spaced "one-per-corner-hole" patterns of physisorption (three cases-directly observed here) and subsequent chemisorption (four cases observed). The patterns were observed by ultrahigh vacuum scanning tunneling microscopy for four different brominated hydrocarbon adsorbates; 1,2-dibromoethane, 1-bromopropane, 1-bromopentane, and bromobenzene, deposited individually on the surface. In every case, adsorbates were overwhelmingly more likely to be found singly than multiply adjacent to a corner-hole, constituting a distinctive pattern having a probability p = 7 Â 10 À5 compared to a random distribution.
The Journal of Chemical Physics, 1972
It has been known for some time from infrared chemiluminescence experiments that a nonthermal rot... more It has been known for some time from infrared chemiluminescence experiments that a nonthermal rotational distribution of hydrogen halide peaked initially at high rotational quantum number, J, relaxes to a thermal distribution without generating a peak at intermediate J ...
The Journal of Chemical Physics, 1970
The Journal of Chemical Physics, 1991
ABSTRACT
The Journal of Chemical Physics, 1995
ABSTRACT At ≳1 ML coverage of methyl bromide adsorbed on LiF(100), CH3Br is efficiently ‘‘photoej... more ABSTRACT At ≳1 ML coverage of methyl bromide adsorbed on LiF(100), CH3Br is efficiently ‘‘photoejected’’ by ultraviolet light at 193 nm, with a mean translational energy of ∼0.3 eV; this is termed PEJ(CH3Br). The system CH3Cl/LiF(100) shows no detectable PEJ(CH3Cl) at this wavelength for which CH3Cl does not efficiently absorb UV. Similarly PEJ(CH3Br) ceased to be observable with 248 nm light, at which wavelength CH3Br does not absorb. Both observations indicate that PEJ is adsorbate mediated. If at 193 nm ∼1 ML of CH3Br is adsorbed beneath ∼1 ML of CH3Cl, efficient PEJ(CH3Cl) is observed. With the sequence of layers reversed (i.e., with the actinic layer on top), PEJ(CH3Cl) is largely suppressed. These observations support the model for PEJ proposed previously [I. Harrison et al., J. Chem. Phys. 89, 1498 (1988)] in which photoexcitation of the underlayer leads, by way of electronic‐to‐translational (E→T) transfer, to ejection of the top layer. The angular distribution of the photoejected species is peaked along the surface normal, consistent with repulsion operating between the under‐ and overlayer. The mean conversion of E→T implied by this mechanism is ∼5%, extending to a maximum of 12%. © 1995 American Institute of Physics.
Chemical Physics Letters, 2012
ABSTRACT We have constructed a high-pressure fast-pulse dosing system for use with Scanning Tunne... more ABSTRACT We have constructed a high-pressure fast-pulse dosing system for use with Scanning Tunneling Microscopy (STM). For 1-bromopentane on Si(1 1 1)-7 × 7 at low temperature (100 K) two physisorbed phases were found to co-exist; spaced-out molecules above corner silicon-adatoms in a one-per-corner-hole (OPCH) pattern, and circles of molecules above middle-adatoms. By tuning the parameters of high-pressure fast-pulse dosing, we can choose which of these two patterns, OPCH or circles, to chemically imprint on room temperature silicon.
Chemical Physics Letters, 1984
State-selective detection of molecular hydr~en by VUV laser-induced fiuorescence has been achieve... more State-selective detection of molecular hydr~en by VUV laser-induced fiuorescence has been achieved at excitation wavelengths greater than the bthium ftuoride cutoff , using xenon as the non-linear medrum-With this approach sensitivities of 010' per cm3 per quantum state have been achieved under cell conditions. This method provides a simple approach to monitoring the vibrational state distribution of hydrogen and its isotopes.
Chemical Physics Letters, 1974
Abstract The infrared chemiluminescence technique has been used to obtain k(V′, R′, T′) (V′, R′, ... more Abstract The infrared chemiluminescence technique has been used to obtain k(V′, R′, T′) (V′, R′, Tt are product vibrational, rotational and translational energies) for the reactions (i) H + ClNO → HCl + NO (energy-release E tot ′ = 68.5 kcal mole −1 ) and (ii) H + CII → HCl + I ( E tot ′ = 55.8 kcal mole −1 ). Reaction (i) exhibits inefficient conversion of energy-release into vibration in the new bond, characteristic of a light attacking atom reacting on a repulsive energy-surface. Reaction (ii) has a bimodal HCl product-energy-distribution suggesting that 18% of the reaction proceeds by direct attack at the Cl end of CII to yield low V ′ and R ′, and 82% by indirect reaction from the 1 end to give high V ′ and R ′.
Chemical Physics, 1976
The iirst test of the information-theoretic approach to branching ratios has been made for the re... more The iirst test of the information-theoretic approach to branching ratios has been made for the reaction: I:+HD-HF;(Y',R')+D-DI?(V'.R.)+H. The vibrational (V') and rotational (R') product energy-distribctions TOI both branches of this reaction have been obtained by the infrared chemiluminesccnce tcchniquc, and have been used in the calculation of an information-theoretic bmnching ratio, reap = 1.41 f 0.18. This is in excellent a@ecment with the esperimentally measured branching ratio of 1.45. However, results from &ssical trajectory calculations raise a question as LO the siplifrcance of this agreement. Classical trajectory calculations (on various energy-surfaces) predict an increase in I' with reagent J. The information-theoretic analysis applied to the product energy-distributions from these trajectory calculations leads IO a qualitatively different result. As D passiblc alternative to the information-theoretic view. simple kinematic features arc noted which could account ror I' > 1. as well as for the sipnilicant differences in product energy-distribution. On this alternative view, the two features arc not indisolubly linked-the exlenl to which they appear in conjunction will depend on the nature of the energy surlace.
Applied Optics, 1983
HCl and HBr lasers have been developed using a short-length-cavity TEA (transverse electric disch... more HCl and HBr lasers have been developed using a short-length-cavity TEA (transverse electric discharge at near atmospheric pressure) laser design. The use of preionization was found to yield reliable operation with pulse-to-pulse stability of better than 5 percent. These lasers were found to run efficiently in both multiline and single-line operation. Measurements in multiline operation showed maximum output energies of
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Papers by John C . Polanyi