i2spec¶
i2spec is an open model of the B³Π(0u⁺) ← X¹Σg⁺ absorption spectrum of molecular iodine. It gives the position, strength and hyperfine structure of every rovibronic line of ¹²⁷I₂, ¹²⁹I₂ and ¹²⁷I¹²⁹I between the B-state dissociation limit (499 nm) and the near infrared, and an uncertainty for each position.
All quantities are computed from a Hamiltonian:
- level energies from the radial Schrödinger equation with potential-energy curves for X and B;
- hyperfine components from an effective nuclear-spin Hamiltonian;
- line strengths from an electronic transition-moment function and the vibrational wavefunctions.
Measured line positions are used in two ways only: as the data to which the potentials and level corrections are fitted, and to estimate the uncertainty of each predicted position.
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Search a wavelength or frequency range; plot the absorption cross section or the transmission of a cell; list the lines with their hyperfine components, uncertainties and measurements.
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Command line, terminal browser, local web server and Python interface.
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Hamiltonians, potentials, numerical methods, intensities and uncertainty estimates.
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All measured data sets used by the model, with links to the original publications.
The model¶
The model combines:
- the X and B potentials of Salumbides et al. (2008), a collaboration of the Amsterdam (VU) and Hannover groups, referred to here as the 2008 potentials, within the range of their fit (X v″ ≤ 17, B v′ ≤ 43);
- Morse/long-range potentials fitted in this work for the levels outside that range;
- empirical corrections to individual levels, fitted to all frequency-comb-referenced measurements, and near the B dissociation limit (v′ = 51–79) to the Orsay atlas of Gerstenkorn & Luc (1983);
- a Gaussian process that corrects the B levels without data of their own (v′ = 3–35) from the corrected levels around them;
- the published hyperfine parameter formulae, with a table of measured corrections to the B-state parameters.
With these, the precision data sets are reproduced to 0.02–0.3 MHz. The uncertainty of positions elsewhere ranges from below 1 MHz to several GHz, depending on the available data; see Uncertainty estimates.