Spectroscopic studies of AlO in argon matrices

The diatomic species AlO has been isolated in argon at 18 K as an Al+O2 reaction product and shown to produce intense laser induced fluorescence in the visible. An infrared-optical double resonance experiment has established the X state vibrational fundamental at 975 cm−1, one of four possibilities previously proposed from infrared studies. 18O experiments further establish the assignment. The apparent low infrared intensity of the AlO stretch is consistent with a recent ab initio calculation of an oscillator strength of 4×10−7. This anomalously low value is confirmed by comparison of infrared and visible absorption intensities for similar samples. A v′=1 lifetime in excess of 6 ms was directly measured for AlO by the double resonance method. This slow rate of radiative relaxation makes AlO attractive as a probe molecule for vibrational relaxation studies.