Overview of the calculation

Steps

A line list is computed in five steps, once per isotopologue. The result does not depend on temperature and is stored. Spectra for a given temperature and absorption cell are computed from it in a sixth step.

Figure 1. The calculation in six steps, each drawn from the model; the inputs of each step are listed beneath it. (1) Levels of X and B, every sixth v at J = 0. (2) Corrections to the B levels at J′ = 40: per-level fits to comb data (points, 1σ) and the Gaussian process that fills levels without their own data (line and band, v′ = 3–35). (3) The 32–0 band as a Fortrat diagram. (4) The 15 strong hyperfine components of R(56) 32–0 under a 300 K Doppler profile. (5) Band strengths at 300 K for v″ = 0, 1 and 2. (6) The cross section near 532 nm and the transmission of a 10 cm cell at 20 °C.

step	quantity	section
1	level energies E(v, J) of X and B	Rovibrational levels
2	empirical corrections to individual levels	Rovibrational levels
3	positions of all allowed P and R lines	Line positions
4	hyperfine components of each line	Hyperfine structure
5	temperature-independent line strengths	Line intensities and spectra
6	cross section and transmission at a given temperature	Line intensities and spectra

Figure 2. Potential-energy curves of X¹Σg⁺ and B³Π(0u⁺) with their J = 0 vibrational levels, drawn between the classical turning points (all levels of X up to v″ = 17, every second level of B up to v′ = 43, then every third level). Levels outside the range of the 2008 fit (Salumbides et al.) are drawn faint. The arrow marks R(56) 32–0 at 532 nm. X dissociates to two ground-state atoms, I(²P3/2) + I(²P3/2); B dissociates to I(²P3/2) + I(²P1/2).

Notation and units

symbol	meaning
v″, J″	vibrational and rotational quantum numbers of the lower level (X state)
v′, J′	the same for the upper level (B state)
R(J″) v′–v″, P(J″) v′–v″	a line with J′ = J″ + 1 (R branch) or J′ = J″ − 1 (P branch)
ν	wavenumber in cm⁻¹; 1 cm⁻¹ = 29 979.2458 MHz
E″	energy of the lower level above X(v″ = 0, J″ = 0), in cm⁻¹
a1, a2, …	main hyperfine components in order of increasing frequency

Energies of both states are measured from the minimum of the X potential. Wavelengths are vacuum wavelengths unless stated otherwise.