Selecting a spectral database

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Selecting a spectral database

The first step to analyze our spectra is to select a spectral line database. Weeds can access both the JPL database for molecular spectroscopy and the Cologne Database for Molecular Spectroscopy (CDMS). To select a database, type `use in`, followed by the name of the database2. For example:

    [fontsize=\scriptsize]
    LAS90> use in cdms
    I-USE,  cdms (online) selected

or:

    [fontsize=\scriptsize]
    LAS90> use in jpl
    I-USE,  jpl (online) selected

As mentioned already, Weeds makes online queries to the molecular databases. However, it is sometimes helpful to make offline searches in a database, for example if you are on travel with no (or a slow) internet connection. Weeds allows us to download a part of – or even the entire – spectral catalog from a database. This catalog is stored in a local database file, and can be used later for offline searches. Making a local copy of the CDMS database between 80 and 130 GHz is done as follows:

    [fontsize=\scriptsize]
    LAS90> use in cdms
    I-USE,  cdms (online) selected
    LAS90> use out mycdms.db
    LAS90> select /freq 80e3 130e3
    I-SELECT,  128957 lines found in the frequency range 80000.0 to 130000.0 MHz
    LAS90> insert

Depending on the speed of your internet connection and the frequency range you have selected, making a local copy of a database may take from a few seconds to a few tens of minutes, so please be patient! In particular, copying the JPL database may take a while, because of technical limitations with this database; copying the CDMS database is much faster.

Once you have made a local copy of a database, you may select it with the `use in` command, followed by the name of the local database file (`.db`):

    [fontsize=\scriptsize]
    LAS90> use in mycdms.db
    I-USE,  mycdms.db (offline) selected

The `use in` and `use out` commands can be used to build a local database containing lines from different sources (e.g. the CDMS and the JPL), and even lines from a private catalog. See the online documentation for more information.