From left to right the 1640 to 1050 cm^-1 spectra of the PAHs anthracene, pyrene, and benzo[ghi]perylene considered are shown here. A) Spectra of the neutral PAH in argon; B) spectra of the neutral PAH in water ice; C) spectra of the PAH cation in argon; D) spectra of the PAH:H₂O mixture after 5 min of in situ VUV photolysis; and E) spectra showing only the photoproduct features that appear after 5 min of in situ VUV photolysis of the PAH:H₂O ice (spectrum “D” −Y × “B”). The tick marks connected to the top axis indicate the positions of PAH⁺ features measured in argon. The PAH:matrix concentrations and temperatures for the spectra shown in A and B are: Ant:Ar  < 1:1000, 10 K; Py:Ar  <  1:1000, 10 K; B_ghiP:Ar  <  1:1000, 10 K and Ant:H₂O = 1:60, 15 K; Py:H₂O = 1:65, 15 K; B_ghiP:H₂O = 1:60, 15 K. Argon matrix spectra of neutral Ant and Py are reproduced from Hudgins & Sandford (1998a), neutral B_ghiP from Hudgins & Sandford (1998b), ionized Ant from Hudgins & Allamandola (1995b), and ionized Py and B_ghiP from Hudgins & Allamandola (1995a).