Interstellar cloud evolution and the abundance of formaldehyde

The time scale for essentially complete conversion of C+ to CO in interstellar clouds can be comparable to, or greater than, dynamical time scales for evolution; therefore suggesting steady state time independent abundances to be inappropriate. The solutions for the time-dependent carbon chemistry in dense clouds, napproximately-greater-than500 cm-3, indicate that significant amounts of neutral carbon will be present throughout a cloud's lifetime. These nonequilibrium values of C I can explain the relatively large abundances observed for formaldehyde, isotopes of carbon monoxide, and other trace molecules