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The structure of a thin zone-cast film of the hexa-n-dodecyl-substituted hexa-peri-benzocoronene (HBC) has been investigated using grazing incidence X-ray diffraction. A model with an orthorhombic unit cell containing two molecules accounts well for the observations. The molecules are arranged in a "herringbone" structure resembling the packing observed for unsubstituted HBC. The molecular disk planes are oriented perpendicularly to the substrate, rotated by approximately 39° about the film normal. The relatively tong side chains of dodecyl were found to be in an ordered interdigitated state. The aliphatic side chains and the aromatic HBC-cores segregate to form regular vertical domains spanning the film thickness. For in-plane rocking scans a discrete orientation distribution is observed with peaks at regular angle intervals. We interpret this as a grain boundary effect induced by alkyl chain stacking faults. [ABSTRACT FROM AUTHOR]

Smog chambers interfaced with in situ FT-IR detection were used to investigate the kinetics and mechanisms of the Cl atom, OH radical, and O 3 initiated oxidation of ( Z )- and ( E )-1,2-dichloroethene (CHClCHCl) under atmospheric conditions. Relative and absolute rate methods were used to measure k (Cl + ( Z )-CHClCHCl) = (8.80 ± 1.75) × 10 -11 , k (Cl + ( E )-CHClCHCl) = (8.51 ± 1.69) × 10 -11 , k (OH + ( Z )-CHClCHCl) = (2.02 ± 0.43) × 10 -12 , k (OH + ( E )-CHClCHCl) = (1.94 ± 0.43) × 10 -12 , k (O 3 + ( Z )-CHClCHCl) = (4.50 ± 0.45) × 10 -21 , and k (O 3 + ( E )-CHClCHCl) = (1.02 ± 0.10) × 10 -19 cm 3 molecule -1 s -1 in 700 Torr of N 2 /air diluent at 298 ± 2 K. Pressure dependencies for the Cl atom reaction kinetics were observed for both isomers, consistent with isomerization occurring via Cl atom elimination from the chemically activated CHCl-CHCl-Cl adduct. The observed products from Cl initiated oxidation were HC(O)Cl (117-133%), CHCl 2 CHO (29-30%), and the corresponding CHClCHCl isomer (11-20%). OH radical initiated oxidation gives HC(O)Cl as a major product. For reaction of OH with ( E )-CHClCHCl, ( Z )-CHClCHCl was also observed as a product. A significant chlorine atom elimination channel was observed experimentally (HCl yield) and supported by computational results. Photochemical ozone creation potentials of 12 and 11 were estimated for ( Z )- and ( E )-CHClCHCl, respectively. Finally, an empirical kinetic relationship is explored for the addition of OH radicals or Cl atoms to small alkenes. The results are discussed in the context of the atmospheric chemistry of ( Z )- and ( E )-CHClCHCl.

Long path length FTIR-smog chamber techniques were used to study the title reactions in 700 Torr of N 2 , oxygen or air diluent at 296 ± 2 K. Values of k (Cl + CF 3 CN) = (2.43 ± 0.33) × 10 -15 and k (OH + CF 3 CN) = (4.61 ± 0.34) × 10 -15 cm 3 molecule -1 s -1 were measured. There was no discernible reaction of CF 3 CN with O 3 and an upper limit of k (O 3 + CF 3 CN) ≤ 7.9 × 10 -24 cm 3 molecule -1 s -1 was established. The IR spectra of CF 3 CN and CF 3 CF 2 CN are reported. The atmospheric lifetime of CF 3 CN is determined by the reaction with OH and is approximately 6.9 years. Reaction of CF 3 CN with Cl atoms in a chamber study gives ( Z -) and/or ( E -) CF 3 CClNCl and CF 3 C(O)Cl as major primary products. Under environmental conditions, the OH radical initiated oxidation gives COF 2 in a yield of (96 ± 8)%. The global warming potential for CF 3 CN is estimated as 1030 for a 100 year time horizon.

The loss of a Cl atom from metastable CH 2 Cl 2 + in the mass-analyzed ion kinetic energy experiment is characterized by a borderline zero kinetic energy release and large kinetic isotope effects on chlorine and hydrogen. Ab initio calculations are employed to assist the interpretation in terms of a nonadiabatic reaction involving electronic predissociation of the electronically excited state 2 A 1 and two-dimensional reaction dynamics. Strong curvature in the reaction coordinate leads to a bobsled effect that accounts for the low kinetic energy release. The kinetic isotope effects enter via the predissociation rate and are interpreted in terms of vibrational overlap integrals.

The chemical mechanisms of the OH radical, Cl-atom and O3 initiated oxidation of (Z)-CF3CH[double bond, length as m-dash]CHCl were studied at 296 ± 1 K in 10-700 Torr air of N2/O2 diluent. Cl atoms add to the [double bond splayed left]C[double bond, length as m-dash]C[double bond splayed right] double bond: 12 ± 5% to the terminal carbon and 85 ± 5% to the central carbon. In 700 Torr of air the products are CF3CHClCHO, HCOCl, CF3COCl, CF3CHO, (E)-CF3CH[double bond, length as m-dash]CHCl, CF3C(O)CHCl2, and CF3CHClCOCl. The yield of (E) isomer was dependent on total pressure, but independent of O2 partial pressure; consistent with isomerization occurring via Cl atom elimination from the chemically activated rather than the thermalized CF3CHCHCl-Cl adduct. The rate constant for (Z)-CF3CH[double bond, length as m-dash]CHCl + Cl was measured at low pressure (10-15 Torr) and found to be indistinguishable from that determined at 700 Torr total pressure, whereas the low pressure rate constant for (E)-CF3CH[double bond, length as m-dash]CHCl was 36% smaller. G4MP2 ab initio calculations showed that the (E) isomer is 1.2 kcal mol-1 more stable than the (Z) isomer. Cl atom elimination from the adduct will preferentially form the (E) isomer and hence the rate of CF3CH[double bond, length as m-dash]CHCl loss will be more sensitive to pressure for the (Z) than the (E) isomer. Reaction of (Z)-CF3CH[double bond, length as m-dash]CHCl with OH radicals gives CF3CHO, HCOCl, (E)-CF3CH[double bond, length as m-dash]CHCl, and HCl. A significant chlorine atom elimination channel was observed experimentally, and supported by computational results. The oxidation products of the reaction of O3 with (Z)- and (E)-CF3CH[double bond, length as m-dash]CHCl were determined with no evidence of isomerization. The results are discussed with respect to the atmospheric chemistry and environmental impact of (Z)- and (E)-CF3CH[double bond, length as m-dash]CHCl.

The atmospheric fates of Z- and E-CF 3 CH[double bond, length as m-dash]CHCF 3 have been studied, investigating the kinetics and the products of the reactions of the two compounds with Cl atoms, OH radicals, OD radicals, and O 3 . FTIR smog chamber experiments measured: k(Cl + Z-CF 3 CH[double bond, length as m-dash]CHCF 3 ) = (2.59 ± 0.47) × 10 -11 , k(Cl + E-CF 3 CH[double bond, length as m-dash]CHCF 3 ) = (1.36 ± 0.27) × 10 -11 , k(OH + Z-CF 3 CH[double bond, length as m-dash]CHCF 3 ) = (4.21 ± 0.62) × 10 -13 , k(OH + E-CF 3 CH[double bond, length as m-dash]CHCF 3 ) = (1.72 ± 0.42) × 10 -13 , k(OD + Z-CF 3 CH[double bond, length as m-dash]CHCF 3 ) = (6.94 ± 1.25) × 10 -13 , k(OD + E-CF 3 CH[double bond, length as m-dash]CHCF 3 ) = (5.61 ± 0.98) × 10 -13 , k(O 3 + Z-CF 3 CH[double bond, length as m-dash]CHCF 3 ) = (6.25 ± 0.70) × 10 -22 , and k(O 3 + E-CF 3 CH[double bond, length as m-dash]CHCF 3 ) = (4.14 ± 0.42) × 10 -22 cm 3 molecule -1 s -1 in 700 Torr of air/N 2 /O 2 diluents at 296 ± 2 K. E-CF 3 CH[double bond, length as m-dash]CHCF 3 reacts with Cl atoms to give CF 3 CHClC(O)CF 3 in a yield indistinguishable from 100%. Z-CF 3 CH[double bond, length as m-dash]CHCF 3 reacts with Cl atoms to give (95 ± 10)% CF 3 CHClC(O)CF 3 and (7 ± 1)% E-CF 3 CH[double bond, length as m-dash]CHCF 3 . CF 3 CHClC(O)CF 3 reacts with Cl atoms to give the secondary product CF 3 C(O)Cl in a yield indistinguishable from 100%, with the observed co-products C(O)F 2 and CF 3 O 3 CF 3 . The main atmospheric fate for Z- and E-CF 3 CH[double bond, length as m-dash]CHCF 3 is reaction with OH radicals. The atmospheric lifetimes of Z- and E-CF 3 CH[double bond, length as m-dash]CHCF 3 are estimated as 27 and 67 days, respectively. IR absorption cross sections are reported and the global warming potentials (GWPs) of Z- and E-CF 3 CH[double bond, length as m-dash]CHCF 3 for the 100 year time horizon are calculated to be GWP 100 = 2 and 7, respectively. This study provides a comprehensive description of the atmospheric fate and impact of Z- and E-CF 3 CH[double bond, length as m-dash]CHCF 3 .

The first study of pseudo-bimolecular cycloaddition reaction dynamics in the gas phase is presented. We used femtosecond time-resolved photoelectron spectroscopy (TRPES) to study the [2+2] photocycloaddition in the model system pseudo-gem-divinyl[2.2]paracyclophane. From X-ray crystal diffraction measurements we found that the ground-state molecule can exist in two conformers; a reactive one in which the vinyl groups are immediately situated for [2+2] cycloaddition and a nonreactive conformer in which they point in opposite directions. From the measured S(1) lifetimes we assigned a clear relation between the conformation and the excited-state reactivity; the reactive conformer has a lifetime of 13 ps, populating the ground state through a conical intersection leading to [2+2] cycloaddition, whereas the nonreactive conformer has a lifetime of 400 ps. Ab initio calculations were performed to locate the relevant conical intersection (CI) and calculate an excited-state [2+2] cycloaddition reaction path. The interpretation of the results is supported by experimental results on the similar but nonreactive pseudo-para-divinyl[2.2]paracyclophane, which has a lifetime of more than 500 ps in the S(1) state., (Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

We have investigated the processes induced by femtosecond laser pulses in chloroamines, with a focus on the generation and observation of a highly reactive radical and on the involvement and general importance of excited-state ions in time-resolved mass spectrometry investigations of gaseous molecules. We have found that 280 nm femtosecond pulses lead to an ultrafast breakage of the N-Cl bond on the repulsive S1 surface, and that resulting radical is long-lived. When exposing the molecule to 420 nm photons a multiphoton ionization takes place to generate ions; these ions can then be excited with a 280 nm photon. The evidence is unambiguous since we observe a distinct temporal evolution of the ion current with no photoelectrons to match. We suggest that the involvement of excited-state ions is a general phenomenon in time-resolved photoionization studies.

We have performed ab initio calculations to examine the potential energy along the normal modes of ground-state HCHO and along the reaction coordinates for loss of H2 and atomic hydrogen, respectively. This exploration showed that there are no specific features that will lead to reaction on the excited-state surfaces for excitations that are relevant to the troposphere and stratosphere. The calculations did however lead to the localization of a conical intersection point through which a specific loss of H2 could take place. However, the conical intersection lies at 5.4 eV relative to the ground state molecule at equilibrium and is thus inaccessible via single photon excitation at tropospheric and stratospheric wavelengths. In addition to the ab initio investigation we have carried out a femtosecond pump-probe experiment using a 266/400 nm excitation. The results show that the timescale for the internal conversion from the initially prepared high-lying Rydberg states is on the order of a picosecond. This process populates the n --> pi* first excited singlet state which then survives for a substantially longer time before it is depopulated to form hot ground state or triplet-excited molecules that can then decompose.

We present high-level computational predictions regarding a novel uncatalysed, yet feasible, C-C bond forming reaction.

The structure of a thin zone-cast film of the hexa-n-dodecyl-substituted hexa-peri-benzocoronene (HBC) has been investigated using grazing incidence X-ray diffraction. A model with an orthorhombic unit cell containing two molecules accounts well for the observations. The molecules are arranged in a "herringbone" structure resembling the packing observed for unsubstituted HBC. The molecular disk planes are oriented perpendicularly to the substrate, rotated by approximately 39 degrees about the film normal. The relatively long side chains of dodecyl were found to be in an ordered interdigitated state. The aliphatic side chains and the aromatic HBC-cores segregate to form regular vertical domains spanning the film thickness. For in-plane rocking scans a discrete orientation distribution is observed with peaks at regular angle intervals. We interpret this as a grain boundary effect induced by alkyl chain stacking faults.

We present structural studies of Langmuir (L) and Langmuir-Blodgett (LB) films of new amphiphilic hexa-peri-hexabenzocoronene (HBC) discotics, carrying five branched alkyl side chains and one polar group. The polar group is either a carboxylic acid moiety or an electron acceptor moiety (anthraquinone). Grazing-incidence X-ray diffraction (GIXD) and X-ray reflectivity, both utilizing synchrotron radiation, show that these amphiphilic HBCs form well-defined Langmuir monolayers at the air-water interface, with a pi-stacked columnar structure where the HBC cores are rotated around the surface normal and tilted relative to the water surface. The intercolumnar distance is 20 A. The HBCs are confined to a layer lying on top of the layer of polar groups that are in contact with the water subphase. Efficient transfer of the monolayer of the anthraquinone-substituted HBC derivative to hydrophobic quartz substrates by vertical dipping gave well-defined multilayer Y-type LB films. Polarized optical spectroscopy, GIXD, and X-ray reflectivity measurements show that the LB films consist of at least two phases. Heating the films results in an irreversible rearrangement to a single macroscopically aligned phase of hexagonally packed columns oriented along the dipping direction with disk planes perpendicular to the columnar axes and stacked in a cofacial manner. This phase transition is analogous to the reversible transition observed in the bulk material.