Photoprocesses in protoplanetary disks

Circumstellar disks are exposed to intense ultraviolet radiation from the young star. In the inner disks, the UV radiation can be enhanced by more than seven orders of magnitude compared with the average interstellar field, resulting in a physical and chemical structure that resembles that of a dense photon-dominated region (PDR). This intense UV field affects the chemistry, the vertical structure of the disk, and the gas temperature, especially in the surface layers of the disk. The parameters which make disks different from traditional PDRs are discussed, including the shape of the UV radiation field, grain growth, the absence of PAHs, the gas/dust ratio and the presence of inner holes. New photorates for selected species, including simple ions, are presented. Also, a summary of available cross sections at Lyman alpha 1216 A is made. Rates are computed for radiation fields with color temperatures ranging from 4000 to 30,000 K, and can be applied to a wide variety of astrophysical regions including exo-planetary atmospheres. The importance of photoprocesses is illustrated for a number of representative disk models, including disk models with grain growth and settling.Comment: A website with the final published version and all photodissociation cross sections and rates can be found at http://www.strw.leidenuniv.nl/~ewine/phot

The Schedule for the Assessment of Drug-Induced Movement Disorders (SADIMoD):Inter-rater reliability and construct validity

The Schedule for the Assessment of Drug-Induced Movement Disorders (SADIMoD) is a newly developed instrument, consisting of a compilation of rating scales, to measure the severity of drug-induced movement disorders: dystonia, dyskinesia, Parkinsonism, akathisia, ataxia, and several types of tremors. The inter-rater reliability and the construct validity of this scale were investigated. Six investigator teams were trained by means of a standard package of instruction material to such an extent that a single member of the team could represent the entire team. Thirty-one patients [20 male/11 female; 57.1 ± 6.5 yr (mean ± S.D.)] with a variety of movement disorders were recorded on videotape according to the SADIMoD Schedule. Single representatives of all six teams scored these video recordings. To this set the existing SADIMoD ratings of 82 patients were added to form the so-called 'total data set'. These patients were examined by 6 different researchers, who rated 4, 8, 10, 14, 18 and 28 patients, respectively, mostly in the context of a research protocol. A specific subset consisted of 12 patients that were examined three times with a two-weekly interval without any change of their medical condition or treatment. The 6 ratings of the 31 individual patients correlated to a highly significant degree, with Kendall's Coefficients of Concordance of 0.436 to 0.891 (median 0.717). The same was true for the 6 ratings of the 7 SADIMoD subscales (median 0.578, range 0.462-0.715) Considering the total data set, the homogeneity of the various subscales was good (Cronbach's χ = 0.81-0.94, median: 0.87). The SADIMoD dyskinesia and dystonia subscales showed a highly significant mutual correlation. The Parkinsonism subscale correlated highly significantly with the rest and postural tremor subscales and to a lesser extent with the akathisia and ataxia subscales. An analysis of variance showed that the three ratings in the subset of 12 patients were not significantly different for any scale. Also Scheffé tests for homogenous subsets did not reveal any significant differences. When investigated under 'real world' circumstances, the inter-rater reliability of the SADIMoD was found to be satisfying. The instruction material, that was developed and used in this study, fully comes up to the requirements. The construct validity of the SADIMoD is more than sufficient.</p

Fine‐Structure Excitation of C + and Si + by Atomic Hydrogen

We present calculations of cross sections for fine-structure excitation in collisions of carbon and silicon ions in the 2P state with atomic hydrogen in the ground state. The results are based on accurate calculations of CH+ and SiH+ molecular potentials, including electronic core correlation and relativistic effects. We find that the energy dependence of the excitation cross sections is largely determined by shape resonances. Our work improves on the results of previous calculations with less accurate potentials. Analytical expressions for the cooling efficiency of C+(2P1/2) and Si+(2P1/2) are given for the temperature interval 15-2000 K.Physic

OH mid-infrared emission as a diagnostic of H

Context. Water is an important molecule in interstellar and circumstellar environments. Previous observations of mid-infrared (IR) rotational lines of OH toward star-forming regions suggest that OH emission may be used to probe the photodissociation of water. Aims. Our goal is to propose a method to quantify H2O photodissociation and measure the local ultraviolet (UV) flux from observations of mid-IR OH lines. Methods. Cross sections for the photodissociation of H2O resolving individual electronic, vibrational, and rotational states of the OH fragment are collected. The state distribution of nascent OH following H2O photodissociation is computed for various astrophysically relevant UV radiation fields (e.g., a single Lyα line or a broadband spectrum). These distributions are incorporated in a new molecular excitation code called GROSBET

Ab Initio Molecular Dynamics Calculations versus Quantum-State-Resolved Experiments on CHD3 + Pt(111): New Insights into a Prototypical Gas–Surface Reaction

The dissociative chemisorption of methane on metal surfaces is of fundamental and practical interest, being a rate-limiting step in the steam reforming process. The reaction is best modeled with quantum dynamics calculations, but these are currently not guaranteed to produce accurate results because they rely on potential energy surfaces based on untested density functionals and on untested dynamical approximations. To help overcome these limitations, here we present for the first time statistically accurate reaction probabilities obtained with ab initio molecular dynamics (AIMD) for a polyatomic gas-phase molecule reacting with a metal surface. Using a general purpose density functional, the AIMD reaction probabilities are in semiquantitative agreement with new quantum-state-resolved experiments on CHD3 + Pt(111). The comparison suggests the use of the sudden approximation for treating the rotations even though CHD3 has large rotational constants and yields an estimated reaction barrier of 0.9 eV for CH4 + Pt(111)