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  • 1
    Electronic Resource
    Electronic Resource
    Photodissociation dynamics of the singlet and triplet states of the NCN radical (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 4923-4932 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The spectroscopy and photodissociation dynamics of the NCN radical have been investigated by fast beam photofragment translational spectroscopy. The B˜ 3Σu−←X˜ 3Σg−, c˜ 1Πu←a˜ 1Δg, and d˜ 1Δu←a˜ 1Δg transitions were examined. The major dissociation products for the B˜ 3Σu− and c˜ 1Πu states are N2(X˜ 1Σg+)+C(3P), while the d˜ 1Δu state dissociates to N2(X˜ 1Σg+)+C(1D). The dissociation channel, N(4S)+CN(X˜ 2Σ+) is observed for the B˜ 3Σu− state at photon energies greater than 4.9 eV, where it comprises (approximate)25±10% of the total signal. At all photon energies, the photofragment translational energy distributions show a resolved progression corresponding to the vibrational excitation of the N2 photofragment. The rotational distributions of the molecular fragments suggest that the dissociation pathway for the N2 loss channel involves a bent transition state while the N+CN photofragments are produced via a linear dissociation mechanism. The P(ET) distributions provide bond dissociation energies of 2.54±0.030 and 4.56±0.040 eV for the N2 and CN loss channels, respectively, yielding ΔHf,0 K(NCN)=4.83±0.030 eV. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479751
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  • 2
    Electronic Resource
    Electronic Resource
    Photodissociation dynamics of the CNN free radical (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 4179-4189 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The spectroscopy and photodissociation dynamics of the A˜ 3Π and B˜ 3Σ− states of the CNN radical have been investigated by fast beam photofragment translational spectroscopy. Vibronic transitions located more than 1000 cm−1 above the A˜ 3Π←X˜ 3Σ− origin were found to predissociate. Photofragment yield spectra for the B˜ 3Σ−←X˜ 3Σ− band between 40 800 and 45 460 cm−1 display resolved vibrational progressions with peak spacing of (approximate)1000 cm−1 corresponding to symmetric stretch 10n and combination band 10n301 progressions. Ground state products C(3P)+N2 were found to be the major photodissociation channel for both the A˜ 3Π and B˜ 3Σ− states. The translational energy distributions for the A˜ 3Π state are bimodal with high and low translational energy components. The distributions for the B˜ 3Σ− state reveal partially resolved vibrational structure for the N2 photofragment and indicate extensive vibrational and rotational excitation of this fragment. These results suggest that bent geometries are involved in the dissociation mechanism and provide more accurate values: ΔfH0(CNN)=6.16±0.05 eV and ΔfH298(CNN)=6.15±0.05 eV. These values, coupled with recent D0(RH) and D298(RH) values from Clifford et al. [J. Phys. Chem. 102, 7100 (1998)], yield ΔfH0(HCNN)=5.02±0.18 eV, ΔfH298(HCNN)=4.98±0.18 eV, ΔfH0(H2CNN)=3.09±0.21 eV, and ΔfH0(H2CNN)=3.09±0.21 eV. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1288267
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  • 3
    Electronic Resource
    Electronic Resource
    Fast beam photodissociation spectroscopy and dynamics of the vinoxy radical (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 3049-3066 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The spectroscopy and photodissociation dynamics of the vinoxy (CH2CHO) radical B˜(2A″) ←X˜(2A″) transition have been investigated by fast beam photofragment translational spectroscopy. We show conclusively that excitation to the B˜ state is followed by predissociation, even for the origin transition. Two photodissociation channels are observed: (1) CH3+CO, and (2) H+CH2CO, with a branching ratio of (approximate)1:4. The form of the translational energy distributions imply a significant exit barrier to formation of CH3+CO, and a considerably smaller barrier for H+CH2CO formation. Dissociation ultimately proceeds by internal conversion to the ground electronic state; the internal conversion rate appears to be significantly enhanced by a curve crossing with either the A˜(2A) or C˜(2A) states. Ab initio calculations of critical points on the global potential energy surfaces aid in determining the dissociation mechanism. We present a simple model for dissociation over a barrier, the statistical adiabatic impulsive model, which satisfactorily reproduces the translational energy distributions. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473419
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  • 4
    Electronic Resource
    Electronic Resource
    Photodissociation spectroscopy and dynamics of the methylthio radical (CH3S) (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 805-816 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The photodissociation spectroscopy and dynamics of the CH3S and CD3S radicals have been investigated using fast radical beam photofragment spectroscopy of the A˜ 2A1←X˜ 2E electronic band (T0≅26 400 cm−1) and an unstructured band near 45 600 cm−1. At all energies, only one major channel, CH3(X˜ 2A2″)+S(3Pj), was observed. Photofragment yield spectra for the A˜ 2A1←X˜ 2E electronic band show resolved vibrational progressions extending well beyond those seen in laser-induced fluorescence studies of this band. Photofragment translational energy distributions yield the S(3Pj) fine-structure distribution for each vibrational level of the CH3 product. Photofragment angular distributions were found to be highly anisotropic (β=−0.2 to −1.0±0.1) with increasing anisotropy at higher photon energies. The results yield a refined heat of formation for CH3S (1.346±0.018 eV) as well as the mechanism by which the A˜ 2A1 state is predissociated. Results at 45 600 cm−1 imply that dissociation occurs on the repulsive B˜ 2A2 state. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478048
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  • 5
    Electronic Resource
    Electronic Resource
    Photodissociation of triplet and singlet states of the CCO radical (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 4070-4078 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The triplet and singlet states of the ketenylidene (CCO) radical are investigated using fast radical beam photofragment translational spectroscopy, in which CCO is generated by laser photodetachment of CCO− and subsequently photodissociated, and anion photoelectron spectroscopy. In the photodissociation experiment, two bands in which the upper state of CCO predissociates are studied. Photodissociation from excitation of the A˜ 3Π–X˜ 3Σ− band in CCO is observed from 16 666–23 529 cm−1; resonances are observed and assigned to excited vibrational levels involving all three vibrational modes. We also report the first observation of the c˜ 1Π–a˜ 1Δ band in CCO. Here, the a˜ 1Δ state of CCO is generated by laser photodetachment at higher photon energy than was used to generate the X˜ 3Σ state. The c˜ 1Π state is approximately located by photoelectron spectroscopy of CCO−, and the photodissociation experiment shows that the origin of the c˜ 1Π–a˜ 1Δ band occurs around 17 170 cm−1. Kinetic-energy release spectra from both bands yield accurate values for the C–CO bond dissociation energy and heat of formation of CCO: D0(C–CO)=2.24±0.02 eV (51.7±0.5 kcal/mol) and ΔHf,2980(CCO)=4.04±0.02 eV (91.1±0.5 kcal/mol). Although the translational-energy distributions resulting from excitation to the A˜ 3Π and c˜ 1Π states are clearly nonstatistical, consideration of the potential-energy surfaces indicates that dissociation from both states occurs via radiationless transitions to the X˜ 3Σ− state. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475839
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  • 6
    Electronic Resource
    Electronic Resource
    Photodissociation spectroscopy and dynamics of the HCCO free radical (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 10087-10098 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The photodissociation spectroscopy and dynamics of the HCCO radical have been investigated using fast radical beam photofragment translational spectroscopy. An electronic band with origin at 33 424 cm−1 has been identified. This band exhibits rotational resolution near the band origin, but the well-defined rovibronic structure is homogeneously broadened at higher photon energies. Based on the rotational structure this band is assigned to the B˜ 2Π←X˜ 2A′′ transition. Photofragment translational energy and angular distributions were obtained at several excitation energies. At excitation energies close to the origin, the excited, spin-forbidden CH(a 4Σ−)+CO channel dominates, while the ground state CH(X 2Π)+CO channel is the major channel at higher photon energies. The translational energy distributions provide evidence of competition between intersystem crossing and internal conversion dissociation mechanisms, with some evidence for nonstatistical dynamics in the CH(X 2Π)+CO channel. This work yields an improved heat of formation for HCCO, ΔHf,2980=1.83±0.03 eV. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474064
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  • 7
    Electronic Resource
    Electronic Resource
    Ultraviolet photodissociation of the HCCO radical studied by fast radical beam photofragment translational spectroscopy (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 6078-6081 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ultraviolet photolysis of jet-cooled mass-selected ketenyl radicals has been investigated using the technique of fast radical beam photofragment translational spectroscopy. The C˜2Π(2A″)–X˜2A″ photofragment yield cross section spans 33 400–48 000 cm−1 and exhibits resolved resonances and broad continua. Dissociation produces both ground and excited state CH radicals in association with ground state CO fragments; there is no evidence for H atom elimination. Analysis of the photofragment kinetic energy release spectra yield a value for the C–C bond dissociation energy and heat of formation of HCCO: D0(HC–CO)=3.14±0.03 eV (72.4±0.7 kcal/mol) and ΔHf,00(HCCO)=1.82±0.03 eV (42.0±0.7 kcal/mol). © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472446
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  • 8
    Electronic Resource
    Electronic Resource
    ON THE SAFETY OF THE PITOCIN DRIP (1958)
    Oxford, UK : Blackwell Publishing Ltd
    BJOG 65 (1958), S. 0 
    Details
    ISSN: 1471-0528
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-0528.1958.tb06211.x
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  • 9
    Electronic Resource
    Electronic Resource
    Characterization of nanometer-scale epitaxial structures by grazing-incidence x-ray diffraction and specular reflectivity (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 1936-1941 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: X-ray rocking curve analysis is a powerful and nondestructive technique for the characterization of heteroepitaxial structures. Conventionally, measurements are performed in symmetrical scattering geometry using a double-crystal x-ray diffractometer but the technique can be extended to the study of very thin layers (〈200 A(ring)) by the use of glancing-incidence scattering geometry and a triple-crystal diffractometer. These structures can also be studied by the technique of total external x-ray reflectivity. This is sensitive to the electron-density profile of the heterostructure as a function of depth. By combining the above techniques we have found it possible to obtain structural information on layers as thin as 20 A(ring). Such measurements permit accurate measurement of individual layer thicknesses and interface roughnesses on the angstrom level. The lattice parameter strain can be obtained by modeling of the intensity distribution of the crystal truncation rod.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.339895
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  • 10
    Electronic Resource
    Electronic Resource
    State-resolved translation energy distributions for NCO photodissociation (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 9020-9027 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The photodissociation dynamics of NCO have been examined using fast beam photofragment translational spectroscopy. Excitation of the 102, 301, and 102302 transitions of the B˜ 2Π←X˜ 2Π band produces N(4S)+CO photofragments exclusively, while excitation of the 103303 transition yields primarily N(2D)+CO photoproducts. The translational energy [P(ET)] distributions yield D0(N–CO)=2.34±0.03 eV, and ΔHf,00(NCO)=1.36±0.03 eV. The P(ET) distributions exhibit vibrationally resolved structure reflecting the vibrational and rotational distributions of the CO product. The N(2D)+CO distribution can be fit by phase space theory (PST), while the higher degree of CO rotational excitation for N(4S)+CO products implies that NCO passes through a bent geometry upon dissociation. The P(ET) distributions suggest that when the B˜ 2Π←X˜ 2Π band is excited, NCO undergoes internal conversion to its ground electronic state prior to dissociation. Excitation of NCO at 193 nm clearly leads to the production of N(2D)+CO fragments. While conclusive evidence for the higher energy O(3P)+CN(X 2Σ+) channel was not observed, the presence of this dissociation pathway could not be excluded. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1369132
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