Near-infrared absorption spectra of 16O3 and 18O3: Adiabatic energy of the 1A2 state?

New absorption spectra of the 1A2(0,v2,1)←1A1(0,0,0) bands of 16O3 and 18O3 near 1 μ are reported. The behavior of vibronic band isotope shifts for low v2 suggests that the lowest point on the 1A2 surface lies 9990±70 cm−1 above the 1A1 minimum. This result is relatively insensitive to the vibrational assignment. Accounting for zero-point and binding energies of the ground state places the 1A2 minimum very close to the O+O2(v=0) dissociation limit, not low enough to support the zero-point energy of a bound state. Implications regarding recent speculation on the role of this and other electronically excited states in ozone photochemistry are discussed.