Because of new telescopes that will dramatically improve our knowledge of theinterstellar medium, chemical models will have to be used to simulate thechemistry of many regions with diverse properties. To make these models morerobust, it is important to understand their sensitivity to a variety ofparameters. In this article, we report a study of the sensitivity of a chemicalmodel of a cold dense core, with homogeneous and time-independent physicalconditions, to variations in the following parameters: initial chemicalinventory, gas temperature and density, cosmic-ray ionization rate, chemicalreaction rate coefficients, and elemental abundances. From the results of theparameter variations, we can quantify the sensitivity of the model to eachparameter as a function of time. Our results can be used in principle withobservations to constrain some parameters for different cold clouds. We alsoattempted to use the Monte Carlo approach with all parameters variedcollectively. Within the parameter ranges studied, the most critical parametersturn out to be the reaction rate coefficients at times up to 4e5 yr andelemental abundances at later times. At typical times of best agreement withobservation, models are sensitive to both of these parameters. The models areless sensitive to other parameters such as the gas density and temperature. Theimprovement of models will require that the uncertainties in rate coefficientsof important reactions be reduced. As the chemistry becomes better understoodand more robust, it should be possible to use model sensitivities concerningother parameters, such as the elemental abundances and the cosmic rayionization rate, to yield detailed information on cloud properties and history.Nevertheless, at the current stage, we cannot determine the best values of allthe parameters simultaneously based on purely observational constraints.
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