TPD spectra (4 K min^-1) obtained after VUV photolysis of an ice mixture containing H₂O:H₂CO=5:1. The photolysis is performed at 13 K for 23 h. Only the relevant m/z values are shown. Detected species are indicated by the letters a-g at their desorption temperature: (a) CH₃OH (m/z 32); (b), (c), (d partial co-desorption between HCOOH (m/z 46), H₂CO₃ (m/z 61), GA (m/z 60), and EG (m/z 62) during water desorption; (e) GA (m/z 60); (f) EG (m/z 62); (g) oligomer of formaldehyde X-(CH₂-O)_n-Y with n< 5.