THE A 3SIGMA-1(U)+]-X-1SIGMA-(G)+ BAND SYSTEMS OF CUAU AND AU2

The a 3Σ+1(u) ← X 1Σ+(g) band systems of jet-cooled CuAu and Au2 have been spectroscopically observed by resonant two-photon ionization spectroscopy. The upper state vibrational constants (ω′e = 109.3 cm-1, ω′eX′e = 0.90 cm-1 for 63Cu197 Au; ω′e = 82.9 cm-1, ω′eX′e = 1.01 cm-1 for 197Au2) indicate shallow excited potential curves, and the long excited state lifetimes (≈ 40 μs for Au2, ≥ 90 μs for CuAu) imply a spin-forbidden decay process, in agreement with the assignment of the transition. Birge-Sponer extrapolations give ground state bond strengths of 2.41 ± 0.07 and 2.290 ± 0.015 eV for CuAu and Au2, respectively. A rotationally resolved scan of 63Cu97 Au has established the bond lengths as r0(X 1Σ+) = 2.3303 ± 0.0009 and r0(a 3Σ+1) = 2.445 ± 0.026 Å. © 1990.