A calculated infrared vibration–rotation spectrum of isotopically modified water, H₂¹⁵O, is presented. Oxygen-15 has a half-life of about 2 minutes and H₂¹⁵O may be formed in the atmosphere during thunderstorms as a result of photonuclear processes or when the atmosphere is irradiated by cosmic γ-rays. Variational nuclear motion calculations of vibrational and vibrational-rotational levels up to 25000 cm⁻¹ and up to J = 10 in angular momentum are performed within the framework of the Born-Oppenheimer approximation using an accurate water potential function. The line shape parameters for H₂¹⁵O are estimated. Spectral ranges that are promising for the detection of H₂¹⁵O in the atmosphere are identified and a search for spectral signatures conducted. A spectral feature is tentatively assigned to the 7₅₂ (0 1 0) - 6₄₃ (0 0 0) line of H₂¹⁵O.