LIDA: The Leiden Ice Database for Astrochemistry

Context. High-quality vibrational spectra of solid-phase molecules in ice mixtures and for temperatures of astrophysical relevance are needed to interpret infrared observations toward protostars and background stars. Such data are collected worldwide by several laboratory groups in support of existing and upcoming astronomical observations. Over the last 25 yr, the Laboratory for Astrophysics at Leiden Observatory has provided more than 1100 (high-resolution) spectra of diverse ice samples.
Aims: In time with the recent launch of the James Webb Space Telescope, we have fully upgraded the Leiden Ice Database for Astrochemistry (LIDA) adding recently measured spectra. The goal of this paper is to describe what options exist regarding accessing and working with a large collection of infrared (IR) spectra, and the ultraviolet-visible (UV/vis) to the mid-infrared refractive index of H₂O ice. This also includes astronomy-oriented online tools to support the interpretation of IR ice observations.
Methods: This ice database is based on open-source Python software, such as Flask and Bokeh, used to generate the web pages and graph visualization, respectively. Structured Query Language (SQL) is used for searching ice analogs within the database and Jmol allows for three-dimensional molecule visualization. The database provides the vibrational modes of molecules known and expected to exist as ice in space. These modes are characterized using density functional theory with the ORCA software. The IR data in the database are recorded via transmission spectroscopy of ice films condensed on cryogenic substrates. The real UV/vis refractive indices of H₂O ice are derived from interference fringes created from the simultaneous use of a monochromatic HeNe laser beam and a broadband Xe-arc lamp, whereas the real and imaginary mid-IR values are theoretically calculated. LIDA not only provides information on fundamental ice properties, but it also offers online tools. The first tool, SPECFY, is directly linked to the data in the database to create a synthetic spectrum of ices towards protostars. The second tool allows the uploading of external files and the calculation of mid-infrared refractive index values.
Results: LIDA provides an open-access and user-friendly platform to search, download, and visualize experimental data of astrophysically relevant molecules in the solid phase. It also provides the means to support astronomical observations; in particular, those that will be obtained with the James Webb Space Telescope. As an example, we analysed the Infrared Space Observatory spectrum of the protostar AFGL 989 using the resources available in LIDA and derived the column densities of H₂O, CO and CO₂ ices.