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A large-scale Breit-Pauli configuration-interaction calculation has been undertaken of all possible 85 E1 optically allowed and intersystem transitions in Sn II among the 22 energetically lowest-lying levels. We have presented a discussion of a sequence of increasingly complex calculations, performed in the LS coupling scheme, in which we have satisfied the necessary criterion in order that we could be confident that a satisfactory convergence of all important valence and core-valence correlation effects had been attained. Judging by the extensive checks we have subjected our results to, we estimate realistic uncertainties in the region of 5% for the stronger transitions studied, achieving an accuracy required for the proposed applications in astrophysical and fusion research. It is encouraging that we can propose possible deficiencies in the theoretical models of previous calculations in an attempt to account for disparities with present data. Although the observed consistency between our results and the greater part of experimental measurements is a comforting indication of reliability, the analysis is not without its discrepancies. We would argue, however, that the present work, representing the most accurate data available to date, warrants further elaborate experimental study. Our calculated fine-tuned oscillator strength for the astrophysically important transition at 1400.5 Å f l = 1.205 ± 0.060 puts into question the conclusions of Sofia et al (Sofia U J, Meyer D M and Cardelli J A 1999 Astrophys. J. 522 L137) that they measured gas-phase ratios of Sn/H in the interstellar medium that appear to be supersolar.

Spectroscopic observation of embedded tin impurity is currently being investigated as a potential diagnostic for monitoring the erosion of vessel wall tiles in fusion power plants (Foster et al 2007 J. Nucl. Mater. 363–5 152), requiring accurate estimates of the oscillator strengths (OS) of the neutral and near-neutral lines. In response to this, we have undertaken (to our knowledge) the first extensive Breit–Pauli configuration-interaction (CI) calculation of transitions in Sn I using the atomic structure code CIV3. Our one-electron functions and configuration basis sets have been carefully selected to represent accurately all important valence and core–valence correlation effects. The reassignments of several LS spectroscopic labels based on our ab initio CI coefficients are suggested, highlighting the substantial inconsistencies in the literature. We invoke various internal checks to demonstrate the accuracy of our ab initio results, validating the decision not to apply our customary fine-tuning technique due to extreme CI mixing of multiple CSFs in a number of LSJ-coupled wavefunctions. The highlighted deficiencies in the results of previous theoretical compilations and the significant scatter observed in the OS measurements obtained from independent experimental methods increase the impetus for own CI calculation, which represents a major improvement in accuracy.

We have undertaken an extensive calculation to obtain the oscillator strengths for all optically allowed and intercombination E1 transitions in Cl I between the fine-structure levels of the odd-parity configurations 3s 2 3p 5 , 3p 4 ( 1 D)4p, 3p 4 ( 3 P)np(4 n 5) and the even-parity configurations 3s3p 6 , 3p 4 ( 3 P, 1 D, 1 S)ns(4 n 5), 3p 4 ( 3 P)6s, 3p 4 ( 3 P, 1 D)3d, 3p 4 ( 3 P)4d, within the Breit-Pauli approximation, using the method of interaction of configurations (CI) enveloped in the general atomic structure code CIV3. The CI wavefunctions have been constructed from a common orthogonal set of 23 one-electron functions (OEFs), which have been carefully selected to ensure that the LS dependency of the orbitals and all important correlation effects have been accurately represented. In the LS-coupling regime, the configuration state functions (CSFs) included in the atomic wavefunction expansions were obtained from all single-and double-electron replacements to the OEFs for each symmetry from the orbitals in the set of dominant configurations 3s 2 3p 5 , 3s3p 6 , 3s 2 3p 4 nl. At the LSJ stage we retain only those CSFs with eigenvector components 0.0005 in magnitude. We then make a further ad hoc refinement to the calculation, whereby the diagonal Hamiltonian matrix elements are adjusted so that the theoretical energy differences coincide with the relevant experimental values. Alternative energy level classifications are proposed for a number of heavily mixed J = 5/2 and J = 3/2 levels based on our calculations, and are supported by the experimental measurements of Schectman et al (1993 Astrophys. J. 406 735). Our results are compared with experimental and available theoretical data. We observe excellent agreement in the length and velocity forms of the oscillator strengths, demonstrating a marked improvement over previous work by Ojha and Hibbert (1990 Phys. Scr. 42 424) and Singh et al (2006 Eur. Phys. J. D 38 285). We predict new oscillator strength data for transitions involving the 3p 4 ( 3 P)5p, 3p 4 ( 3 P)4d, 3p 4 ( 3 P)6s configurations where no other theoretical values are available.

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This paper introduces the use of a multi-variate correlation function for region-based image matching and extends it to a modified crosscorrelation function that works well when matching image areas are required have the same intensity contrast. It also shows that the multivariate case is a straightforward generalisation of the monochrome image case. Experiments with both MRI and RGB colour imagery are shown, along with comparisons with the Euclidean, Manhatten and Loo matching metrics.