Molecular hydrogen is the most abundant molecule in the universe. It is the first one to form
and survive photo-dissociation in tenuous environments. Its formation involves catalytic …

Since we intend to review experimental and theoretical studies of physicochemical
processes occurring on cosmic dust grains in very cold regions in space, we start with a brief …

Molecular absorption and emission bands dominate the visible, infrared, and submillimeter
spectra of most objects with associated gas. These observations reveal a surprisingly rich …

The first detection of molecules in space (CH, CH+, and CN) occurred in the late 1930s.
Since then over 180 different molecular species have been detected (http://www …

Molecular hydrogen exists in nuclear-spin isomers of ortho and para species according to
the total nuclear spin. These species are correlated to the rotational states with even and …

Context. Millimetric observations have measured high degrees of molecular deuteration in
several species seen around low-mass protostars. The Herschel Space Telescope …

Prestellar cores form from the contraction of cold gas and dust material in dark clouds before
they collapse to form protostars. Several concurrent theories exist to describe this …

Water has two nuclear-spin isomers: ortho-and para-H 2 O. Some observations of interstellar
space and cometary comae have reported the existence of gaseous H 2 O molecules with …

Interstellar dark clouds are the sites of star formation. Their main component, dihydrogen,
exists under two states, ortho and para. H 2 is supposed to form in the ortho: para ratio …

Context. Fast surface conversion between ortho-and para-H 2 has been observed in
laboratory studies, and it has been proposed that this mechanism plays a role in the control …