Formaldehyde thermal evolution as a function of temperature in water ice containing CH₃NH₂¹⁴N (triangle), and ¹⁵N (square) (H₂O/CH₃NH₂/CH₂O = 1/2/0.1). The rate coefficients are given in the form k = ν₀exp( − E/RT), where T is the ice temperature (K), ν₀ the pre-exponential factor (s^-1), and E the activation energy (J mol^-1). The corresponding rate coefficients are k_14N = 1.5 ± 0.1 × 10^-2exp( − 1100 ± 50/RT) and k_15N = 2.6 ± 0.3 × 10^-2exp( − 1800 ± 80/RT).