[ARTS-2.6] fix: correct Wigner-3j m-index ordering in reduced_rovibrational_dipole#1133
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reduced_rovibrational_dipole used the wrong Wigner-3j m-index ordering (li, lf-li, -lf instead of lf, li-lf, -li). The resulting rigid-rotor dipole Dipo0 disagrees with the values stored in the HITRAN line-mixing band data files (and the Lamouroux LM_calc_CO2.for reference), which corrupts the relaxation-matrix sum-rule correction in calcw. For the fundamental band (li=0) the two orderings nearly agree, so it was unaffected; for hot bands (li=1,2,3) at low J the magnitudes differ by factors of 2-6x, producing the wrong-sign and 5-25x inflated first-order Rosenkranz Y values reported in atmtools#1130. Use the correct m-ordering, matching the file Dipo0 to ~2e-8 across all P/Q/R lines of the affected bands. Fixes atmtools#1130.
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This looks great. Can you also push the fix to ARTS3? The code there is just called "reduced_dipole" |
riclarsson
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Jun 22, 2026
riclarsson
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Swap the m-arguments passed to wigner3j in reduced_dipole so the second triplet matches the intended (lf, li-lf, -li) ordering rather than (li, lf-li, -lf). Same fix as for ARTS 2.6 in PR #1133.
riclarsson
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Fixes an incorrect argument ordering in the Wigner 3j symbol computed inside `reduced_dipole` within the Hartmann ECS line-shape model. The previous call swapped the `(li, lf - li, -lf)` triplet with `(lf, li - lf, -li)`, producing wrong reduced dipole values and thus erroneous scaling of relaxation-matrix off-diagonal elements. The corrected arguments restore the physically intended coupling for the rotational quantum numbers. Same fix as in ARTS 2.6 PR #1133. ### Changes - `src/core/lbl/lbl_lineshape_voigt_ecs_hartmann.cpp`: Updated both branches of the `iseven(Jf + lf + 1)` conditional in `reduced_dipole` to call `wigner3j(Jf, k, Ji, lf, li - lf, -li)` instead of `wigner3j(Jf, k, Ji, li, lf - li, -lf)`, ensuring the bra-side and ket-side angular momentum couplings are passed in the correct order. ### Breaking Changes None — this is a bug fix. Results previously computed with the Hartmann ECS line-shape model for affected transitions will change numerically to the correct values.
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This PR fixes a sign and magnitude error in the
reduced_rovibrational_dipolefunction that produced wrong-sign and inflated first-order Rosenkranz Y coefficients for HITRAN CO2 line-mixing hot bands. The rigid-rotor dipole was computed with the incorrect Wigner-3j magnetic-index ordering (li, lf-li, -lfinstead oflf, li-lf, -li), causing the relaxation-matrix sum-rule correction incalcwto be corrupted. The fundamental band (li=0) was largely unaffected because both orderings nearly agree, but hot bands (li=1,2,3) at low J saw magnitudes differ by factors of 2–6x.Changes
src/absorptionlines.cc: Corrected thewigner3jarguments inAbsorption::reduced_rovibrational_dipoleto use the proper m-index ordering (lf, li-lf, -li), aligning the computedDipo0with the values stored in HITRAN line-mixing band data files and the LamourouxLM_calc_CO2.forreference to ~2e-8 across all P/Q/R lines.Before/after comparison with script from #1130:
Breaking Changes