Installation and usage

i2spec is a Python package managed with uv. The first uv run command creates the environment and installs the dependencies.

git clone https://github.com/mgrau/i2spec.git
cd i2spec
# terminal browser (also: uv run i2spec)
uv run i2spec tui
# line explorer and documentation, at http://localhost:8777
uv run i2spec web

The first query for an isotopologue computes its line list, which takes a few minutes and is then cached in ~/.cache/i2spec. The first i2spec web also exports the model data used by the line explorer to web/data/.

Command line

# all lines in a range, with uncertainties
uv run i2spec lines 532.2 532.3
# in cm-1, the ten strongest
uv run i2spec lines 18788 18789 --unit cm-1 \
    --sort strength --limit 10
# another isotopologue, as JSON
uv run i2spec lines 632.9 633.0 -i 129I2 --json
# one line with its hyperfine components
uv run i2spec line "R(56) 32-0"

Ranges can be given in nm (vacuum wavelength), nm-air, cm-1, THz or MHz. Line strengths are integrated cross sections in cm per molecule at the chosen temperature (option -T, default 293.15 K).

Terminal browser

uv run i2spec tui shows the absorption spectrum of the selected range, the list of lines, and the hyperfine components of the selected line.

key	action
+ / -	zoom the spectrum in or out
[ / ]	move the spectrum window
c	centre the spectrum on the selected line
l	logarithmic intensity scale
p	line profile: Doppler-broadened or sub-Doppler (Lamb dips and crossover resonances)
s	sort the list by strength
a	include the weak ΔF ≠ ΔJ components
/	return to the search field

Line explorer and documentation

# build the site and serve it on this computer
uv run i2spec web
# serve it on the local network as well
uv run i2spec web --lan
# re-export the model data after a change to the model
uv run i2spec web export
# write the static site to site/
uv run i2spec web build site
# preview this documentation while editing it
uv run mkdocs serve

Python interface

from i2spec import MHZ_PER_CM, RovibronicModel

m = RovibronicModel("127I2")
# R(56) 32-0, hyperfine-free position in cm⁻¹
nu = m.transition(32, 0, 56, "R")
# 18788.3355 cm⁻¹, 563 260 129 MHz
print(nu, nu * MHZ_PER_CM)

# nu0 and the component offsets in MHz
nu0, comps = m.hyperfine_components(32, 0, 56, "R")
a10 = next(c for c in comps if c.label == "a10")
# 563 260 223.52 MHz (CIPM value: 563 260 223.513 MHz)
print(nu0 + a10.offset)

i2spec.lookup.Catalog returns line lists at any temperature, i2spec.spectrum computes cross sections and cell transmission, and i2spec.continuum computes the bound–free absorption.

Tests

# Python test suite
uv run pytest
# line explorer against the Python model
node web/test_physics.mjs
# redraw the documentation figures
uv run --group research python \
    documentation/figures/make_figures.py