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The photodissociation of CH3I in the blue edge (217–230 nm) of the A-band has been studied using a combination of slice imaging and resonance enhanced multiphoton ionization (REMPI) detection of the CH3fragment in the vibrational ground state (ν= 0). The profiles of the CH3(ν= 0) kinetic energy distributions and the photofragment anisotropies are interpreted in terms of the contribution of the excited surfaces involved in the photodissociation process, as well as the probability of non-adiabatic curve crossing between the 3Q0and 1Q1states. In the studied region, unlike in the central part of the A-band where absorption to the 3Q0state dominates, the I(2PJ), with J= 1/2, 3/2, in correlation with CH3(ν= 0) kinetic energy distributions show clearly two contributions of different anisotropy, signature of the competing adiabatic and non-adiabatic dynamics, whose ratio strongly depends on the photolysis wavelength. The experimental results are compared with multisurface wave packet calculations carried out using the available ab initiopotential energy surfaces, transition moments, and non-adiabatic couplings, employing a reduced dimensionality model. A good qualitative agreement is found between experiment and theory and both show evidence of reverse 3Q0← 1Q1non-adiabatic dynamics at the bluest excitation wavelengths both in the fragment kinetic energy and angular distributions. [ABSTRACT FROM AUTHOR]

The photodissociation dynamics of pyrrole–ammoniaclusters (PyH·(NH3)n, n = 2–6) has been studied using a combination of velocity map imaging and non-resonant detection of the NH4(NH3)n−1 products. The excited state hydrogen-atom transfer mechanism (ESHT) is evidenced through delayed ionization and presents a threshold around 236.6 nm, in agreement with previous reports. A high resolution determination of the kinetic energy distributions (KEDs) of the products reveals slow (∼0.15 eV) and structured distributions for all the ammoniacluster masses studied. The low values of the measured kinetic energy rule out the existence of a long-lived intermediate state, as it has been proposed previously. Instead, a direct N–H bond rupture, in the fashion of the photodissociation of bare pyrrole, is proposed. This assumption is supported by a careful analysis of the structure of the measured KEDs in terms of a discrete vibrational activity of the pyrrolyl co-fragment. [ABSTRACT FROM AUTHOR]

Abstract: Wave packet simulations of the CD3I photodissociation dynamics in the A band are reported, and the isotope effect in several time-dependent and asymptotic properties is analyzed for different dissociation channels. The reaction times are found to be only about 7–8fs longer than in the case of CH3I photodissociation. The isotope effect manifests itself strongly in a higher internal excitation of CD3 compared to CH3, which is exhibited in the vibrational, rotational, and translational energy distributions of the CD3 fragments, particularly in the CD3 +I(2P3/2) dissociation channel. [Copyright &y& Elsevier]

Erika Bowker and colleagues dispel some of the misconceptions about nursing in the independent sector by describing initiatives developed at an independent London hospital. [ABSTRACT FROM AUTHOR]

This paper describes crossed beam experiments and quasiclassical trajectory (QCT) calculations for the ‘insertion’ reaction O( 1 D )+D2 at a collision energy ( Ec =25.9?kJ?mol -1 ) much higher than the calculated barrier (~8.4?kJ?mol -1 ) for the competitive ‘abstraction’ mechanism, which takes place along the excited state potential energy surfaces (PES). Adiabatic QCT calculations were carried out on the ground 1 1 A ' and first excited 1 1 A '' PESs developed by Dobbyn and Knowles. Non-adiabatic contributions from the excited 2 1 A ' PES to the reaction were considered by means of a trajectory surface hopping method. QCT calculations were also performed at Ec =22.2?kJ?mol -1 to compare with previous experimental results. Excellent agreement was found between experiment and QCT predictions at Ec =22.2?kJ?mol -1 , while at the higher Ec of 25.9?kJ?mol -1 only a qualitative agreement was noted. In all cases, the comparison was significantly improved with respect to QCT calculations on a previous version of the ground state PES. [ABSTRACT FROM AUTHOR]

Progress in the understanding of the H  +  H2 reaction and its isotopic variants is reviewed with special attention to the achievements of the last decade. The detailed agreement between theory and experiment attained during this period is emphasized and major experimental and theoretical advances are highlighted. The excellent description of most experimental findings, from state-resolved cross sections to thermal rate constants, provided by the available quantum mechanical treatments, as well as the good overall behaviour of classical mechanics are underlined. Debated issues on short-lived complexes and delayed scattering, resonances and interferences, or geometric phase effects are extensively discussed. Finally, the state-of-the-art is summarized and prospects for future research on this prototypic system are presented. [ABSTRACT FROM AUTHOR]

The rotational relaxation of N2 in collisions with He has been investigated in free jets with a combination of resonance-enhanced-multiphoton ionization spectroscopy and time-of-flight techniques. From the measured data, a global cross-section for rotational relaxation has been derived. The cross section grows from a value of ≈8 A˚2 at 100 K to ≈18 A˚2 at 5–15 K. For the weakest supersonic expansions investigated, a breakdown of the translational equilibrium between He and N2 has been observed, that could be well accounted for by an isentropic jet model and classical collision cross-sections. [Copyright &y& Elsevier]

Abstract: The N(2 D)+H2(v =0, j =0) reaction and its HD and D2 isotopic variants have been studied by means of quantum mechanical real wave packet and wave packet with split operator and quasiclassical trajectory methodologies on the potential energy surface of Ho et al. [J. Chem. Phys. 119 (2003) 6]. Total initial state-selected and final state-resolved reaction probabilities and product rotational distributions have been calculated for total angular momentum J =0 in a broad range of collision energies. The real wave packet results are in very good agreement with the corresponding split operator wave packet calculations. A reasonable overall good agreement has been found between the wave packet and quasiclassical trajectory results. Integral cross-sections and thermal rate constants have been calculated from the wave packet reaction probabilities by means of standard J-shifting, refined J-shifting and uniform J-shifting methods in combination with the centrifugal sudden approximation for J >0. Comparisons with available exact wave packet, quasiclassical trajectory and experimental results are made and discussed. [Copyright &y& Elsevier]

The alignment of CD3 fragments following the photodissociation of fully deuterated dimethyl sulfide (CD3SCD3) on the first absorption band (at 219 nm) has been characterised using (2 + 1) resonance-enhanced multiphoton ionization (REMPI) spectroscopy. Operation of the time-of-flight (TOF) mass spectrometer with a low ion extraction field rejects off-axis travelling CD3 fragments, allowing velocity-selected REMPI spectra to be obtained. The strong dependence of the REMPI signal on the polarization of the probe laser is adequately explained by an impulsive model dissociation where the fragments recoil axially along the CD3S–CD3 bond. In general, the methyl fragments are found to be preferentially spinning about their C3 axis after photodissociation, correlating with zero-point torsional vibrational motion of the parent molecule. [Copyright &y& Elsevier]