Pulsed-laser ablated beryllium atoms codeposited with O-2 in excess argon at 10 K yielded new beryllium-oxygen molecules. The initial reaction to make BeO is endothermic, but activation energy is provided by hyperthermal Be atoms. A strong band at 1572.9 cm(-1) and a weak band at 398.9 cm(-1) gave oxygen isotopic shifts consistent with a BeO diatomic molecule and are assigned to the O-2-BeO complex analogous to the Ar-BeO complex. A sharp band at 1413.2 cm(-1) exhibited an oxygen isotopic triplet with O-16,18(2) and shifts appropriate for linear OBeO. A nearly coincident band at 1412.4 cm(-1) gave an isotopic doubler and shifted in agreement with linear BeOBe. Quantum chemical calculations at the second-order many-body perturbation theory [MBPT(2)] level predict (3) Sigma ground states and nu(3) fundamentals at 1422.5 and 1418.2 cm(-1) for OBeO and BeOBe, respectively, in excellent agreement with the observed values. Three bands at 1131.2, 866.3, and 522.4 cm(-1) increased together on photolysis, yielded isotopic triplets, and agreed with MBPT(2) calculations for rhombic Be2O2. A sharp photosensitive band at 988.6 cm(-1) gave oxygen isotopic shifts consistent with another linear OBeO species and is tentatively assigned to the molecular anion. An intense band at 1465.1 cm(-1) that appeared on annealing gave oxygen isotopic shifts in agreement with calculations for linear BeOBeO. Two bands at 1288.9 and 1264.1 cm(-1) appeared on photolysis and gave isotopic triplets and shifts that are in excellent agreement with calculations for branched BeBeO2. Annealing produced bands at 871.8 and 436.1 cm(-1) that decreased on photolysis and are assigned to BeO3.