  Several of NASA missions (TESS, JWST, WFIRST, etc.) and mission concepts
(LUVOIR, HabEx, and OST) emphasize the exploration and characterization of
exoplanets, and the study of the interstellar medium. We anticipate that a much
broader set of chemical environments exists on exoplanets, necessitating data
from a correspondingly broader set of chemical reactions. Similarly, the
conditions that exist in astrophysical environments are very different from
those traditionally probed in laboratory chemical kinetics studies. These are
areas where quantum mechanical theory, applied to important reactions via
well-validated chemical kinetics models, can fill a critical knowledge gap.
Quantum chemical calculations are also introduced to study interior of planets,
photochemical escape, and many critical chemical pathways (e.g. prebiotic
environments, contaminations, etc.) After years of development of the relevant
quantum chemical theories and significant advances in computational power,
quantum chemical simulations have currently matured enough to describe real
systems with an accuracy that competes with experiments. These approaches,
therefore, have become the best possible alternative in many circumstances
where performing experiments is too difficult, too expensive, or too dangerous,
or simply not possible. In this white paper, several existing quantum chemical
studies supporting exoplanetary science, planetary astronomy, and astrophysics
are described, and the potential positive impacts of improved models associated
with scientific goals of missions are addressed. In the end, a few
recommendations from the scientific community to strengthen related research
efforts at NASA are provided.
