5 research outputs found
Insight into the Photodissociation Dynamical Feature of Conventional Transition State and Roaming Pathways by an Impulsive Model
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
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
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
Large-area
and flexible amorphous photonic crystals (APCs) featuring
interconnected network microstructures are fabricated using high-molecular-weight
polystyrene-<i>block</i>-polyÂ(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
Large-area
and flexible amorphous photonic crystals (APCs) featuring
interconnected network microstructures are fabricated using high-molecular-weight
polystyrene-<i>block</i>-polyÂ(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