An automated method for producing multivariate optical element (MOE) interference filters that are robust to errors in the reactive magnetron sputtering process is described. Reactive magnetron sputtering produces films of excellent thickness and uniformity. However, small changes in the thickness of individual layers can have severe adverse effects on the predictive ability of the MOE. Adaptive reoptimization of the filter design during the deposition process can maintain the predictive ability of the final filter by changing the thickness of the undeposited layers to compensate for the errors in deposition. The merit function used, the standard error of calibration, is fundamentally different from the standard spectrum matching. This new merit function allows large changes in the transmission spectrum of the filter to maintain performance.
The fundamental and overtone vibrational absorption spectroscopy of the C–H unit in CHCl3 is measured for transitions from the ν = 0 energy level to ν = 1 through ν = 5 energy levels. The energies of the transitions exhibit a linearly-decreasing spacing between adjacent vibrational levels as the vibrational quantum number increases. These data are used as the basis for Birge–Sponer estimation of the dissociation energy, D
0, for the C–H bond in chloroform. The value obtained from the first 5 transitions is D
0 = 459 ± 8 kJ mol-1 (95% confident interval), compared to a literature value of the bond dissociation energy for this bond of 401 kJ mol-1. The error of 14.5% results from sampling only the most harmonic energy levels in the vibrational potential well.
Rapid quantitative imaging of chemical species is an important tool for investigating heterogenous mixtures, such as laminated plastics, biological samples and vapor plumes. Using traditional spectroscopic methods requires difficult computations on very large data sets. By embedding a spectral pattern that corresponds to a target analyte in an interference filter in a beamsplitter arrangement; the chemical information in an image can be obtained rapidly and with a minimal amount of computation. A candidate filter design that is tolerant to the angles present in an imaging arrangement is evaluated in near-infrared spectral region for an organic analyte and an interferent.
The rotational fine structure observable in a forbidden electronic absorbance of diatomic oxygen in the earth's atmosphere can be observed as a series of minima in the solar spectrum near 762 nm wavelength. The relative intensities of these rotational fine-structure lines can be used quantitatively to estimate the average temperature of the atmosphere along the path taken by sunlight to the observer. Measured values for temperature vary from day to day and season to season and are generally far lower than ambient temperatures because of averaging over the depth of the atmosphere. These experimentally determined thermodynamic temperatures can be compared to Web-based atmospheric models for particular locations and times to illustrate the fact that they are average values.
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