5 research outputs found

    Insight into the Photodissociation Dynamical Feature of Conventional Transition State and Roaming Pathways by an Impulsive Model

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    Without the need to construct complicated potential energy surfaces, a multicenter impulsive model is developed to characterize the dynamical feature of conventional transition state (TS) and roaming pathways in the photodissociation of formaldehyde, H<sub>2</sub>CO → CO + H<sub>2</sub>. The photofragment energy distributions (PED) resulting from the roaming mechanism are found to closely correlate to a particular configuration that lies close to the edge of the plateau-like intrinsic reaction coordinate, whereas such a PED is associated with the configuration at the saddle point when the conventional TS pathway is followed. The evaluated PED results are consistent with those by experimental findings and quasi-classical trajectory calculations. Following impulsive analysis, the roaming pathway can be viewed as a consequence of energy transfer events between several vibrational modes. For H<sub>2</sub>CO, the available energy initially accumulated at the C–H bond is transferred to other transitional mode(s) via stretching-bending coupling, and finally to the HH stretching

    Photodissociation of Propionaldehyde at 248 nm: Roaming Pathway as an Increasingly Important Role in Large Aliphatic Aldehydes

    No full text
    Time-resolved Fourier transform infrared emission spectroscopy is employed in the photolysis of propionaldehyde (CH<sub>3</sub>CH<sub>2</sub>CHO) at 248 nm to characterize the role of the roaming pathway. High-resolution spectra of CO are analyzed to yield a single Boltzmann rotational distribution for each vibrational level (ν = 1–4) with small rotational and large vibrational energy disposals. A roaming saddle point is found containing two far separated moieties of HCO and CH<sub>3</sub>CH<sub>2</sub> with a weak interaction between them. Quasiclassical trajectory calculations on this configuration yield the CO energy flow behavior, consistent with the findings. The rate constant along the roaming pathway is evaluated to be larger by >1–2 orders of magnitude than those along tight transition state or three-body dissociation pathways. This work implies that the roaming mechanism plays an increasingly important role in aliphatic aldehydes as the molecular size becomes larger

    Photodissociation of Propionaldehyde at 248 nm: Roaming Pathway as an Increasingly Important Role in Large Aliphatic Aldehydes

    No full text
    Time-resolved Fourier transform infrared emission spectroscopy is employed in the photolysis of propionaldehyde (CH<sub>3</sub>CH<sub>2</sub>CHO) at 248 nm to characterize the role of the roaming pathway. High-resolution spectra of CO are analyzed to yield a single Boltzmann rotational distribution for each vibrational level (ν = 1–4) with small rotational and large vibrational energy disposals. A roaming saddle point is found containing two far separated moieties of HCO and CH<sub>3</sub>CH<sub>2</sub> with a weak interaction between them. Quasiclassical trajectory calculations on this configuration yield the CO energy flow behavior, consistent with the findings. The rate constant along the roaming pathway is evaluated to be larger by >1–2 orders of magnitude than those along tight transition state or three-body dissociation pathways. This work implies that the roaming mechanism plays an increasingly important role in aliphatic aldehydes as the molecular size becomes larger

    Flexible or Robust Amorphous Photonic Crystals from Network-Forming Block Copolymers for Sensing Solvent Vapors

    No full text
    Large-area and flexible amorphous photonic crystals (APCs) featuring interconnected network microstructures are fabricated using high-molecular-weight polystyrene-<i>block</i>-poly­(methyl methacrylate) (PS–PMMA) block copolymers. Kinetically controlled microphase separation combining with synergistic weak incompatibility gives rise to short-range-order network microstructures, exhibiting noniridescent optical properties. Solubility-dependent solvatochromism with distinct responses to various organic solvent vapors is observed in the network-forming APC film. By taking advantage of photodegradation of the PMMA block, nanoporous network-forming films were prepared for subsequent template synthesis of robust SiO<sub>2</sub>- and TiO<sub>2</sub>-based APC films through sol–gel reaction. Consequently, refractive index contrast of the APC film was able to be manipulated, resulting in intensely enhanced reflectivity and increased response rate for detecting solvent vapor. With the integration of self-assembly and photolithography approaches, flexible and robust network-forming APC films with well-defined photopatterned textures are carried out. This can provide a novel means for the design of photopatterned organic or inorganic APC films for sensing solvent vapors

    Flexible or Robust Amorphous Photonic Crystals from Network-Forming Block Copolymers for Sensing Solvent Vapors

    No full text
    Large-area and flexible amorphous photonic crystals (APCs) featuring interconnected network microstructures are fabricated using high-molecular-weight polystyrene-<i>block</i>-poly­(methyl methacrylate) (PS–PMMA) block copolymers. Kinetically controlled microphase separation combining with synergistic weak incompatibility gives rise to short-range-order network microstructures, exhibiting noniridescent optical properties. Solubility-dependent solvatochromism with distinct responses to various organic solvent vapors is observed in the network-forming APC film. By taking advantage of photodegradation of the PMMA block, nanoporous network-forming films were prepared for subsequent template synthesis of robust SiO<sub>2</sub>- and TiO<sub>2</sub>-based APC films through sol–gel reaction. Consequently, refractive index contrast of the APC film was able to be manipulated, resulting in intensely enhanced reflectivity and increased response rate for detecting solvent vapor. With the integration of self-assembly and photolithography approaches, flexible and robust network-forming APC films with well-defined photopatterned textures are carried out. This can provide a novel means for the design of photopatterned organic or inorganic APC films for sensing solvent vapors
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