Structure and rovibrational analysis of the [O-2((1)Delta(g))(v=0)](2)<-[O-2((3)Sigma(-)(g))(v=0)](2) transition of the O-2 dimer

The rotationally resolved absorption spectrum of the O-2 dimer involving th e [O-2((1)Delta(g))(v=0)](2)<--[O-2((3)Sigma(g)(-))(v=0)](2) transition has been recorded near 632.6 nm by continuous wave Cavity Ring Down Spectrosco py in a supersonic slit jet expansion of pure O-2. A quadratic dependence o f the absorption in the jet versus the stagnation pressure is observed. A r otational temperature of 12 K is derived from the (O-2)(2) rotational analy sis. The high spectral resolution of the CW-CRDS measurements limited by th e residual Doppler broadening in the jet and the low rotational temperature allow the first rotational analysis in this open-shell complex. The same s pectrum was also recorded by Intracavity Laser Absorption Spectroscopy and the comparison of the performances of the two methods is discussed. Among m ore than 600 lines measured between 15 800 and 15 860 cm(-1) from the CW-CR DS spectrum, 40 were assigned to the P-R(0), (R)Q(0), and R-R(0) branches o f two subbands associated with B-1(-)<-- A(1)(+) and A(1)(+)<-- B-1(-) tran sitions between the ground and excited rovibrational levels, labeled follow ing the G(16) permutation inversion representation. Forty five lines were a ssigned to P-P(2), (P)Q(2), and R-P(2) branches of two subbands associated with B-1(-)<-- A(1)(+) and A(1)(+)<-- B-1(-) transitions. The subbands cent ered at 15 808.401(49) [A(1)(+)<-- B-1(-)] and 15 813.134(37) cm(-1) [B-1(- )<-- A(1)(+)] for those arising from K=0, and at 15 812.656(20) [A(1)(+)<-- B-1(-)] and 15 818.277(35) [B-1(-)<-- A(1)(+)] when arising from K=2, are analyzed considering (O-2)(2) as a slightly asymmetric prolate top. The rot ational analysis of the two K=0 subbands leads to very close values of the effective rotational constant, B-p=(B+C)/2, for both A(1)(+) and B-1(-) lev els: 0.095 cm(-1) for the [O-2((3)Sigma(g)(-))(v=0)](2) lower states and 0. 063 cm(-1) for the [O-2((1)Delta(g))(v=0)](2) excited states, in close agre ement with theoretical values. The H geometry is confirmed as the most stab le for the ground electronic singlet state. A distance between the two mono mers of 6.1 a(0) and 7.5 a(0) is derived for the ground and excited singlet states. Similar results are obtained from the two K=2 subbands. A vibratio nal assignment is given for the two rotationally analyzed subbands (K=0) an d proposed for the main features of the whole band. (C) 2000 American Insti tute of Physics. [S0021-9606(00)01614-7].