NOTE
Measurement of the Radiative Lifetime of the CrO( B 5 P V , y Å 0) State
In a recent article, we gave an experimental value of the dissociation (50 V loaded) was connected directly to a transient digitizer (Tektronix TDS 620, 500 MHz band pass, 0.8 nsec rise time, 50 V input) for radiative energy of the CrO molecule, D 0 (CrO) Å 4.74 { 0.09 eV, determined from lifetime measurements. In each run, 256 fluorescence decay traces were a crossed-beam study of the Cr(a 7 S 3 ) / O 2 (X 3 S 0 g ) r CrO(X 5 P V ) / accumulated and then transferred to a computer for signal processing. O( 3 P J ) reaction (1). Following this determination, we now present the first Due to the strong cooling caused by the expansion, CrO molecules could measurement of the radiative lifetimes of the CrO(B 5 P V , £ Å 0) state, be detected only in the lowest rotational levels of the X 5 P, £ Å 0, V Å obtained by pulse-decay method in a collisionless environment.
01, 0, and 1 sub-states. Signal-to-noise considerations precluded any serious The experimental approach is the same as that previously described in analysis of the V Å 2 and 3 spin-orbit components which were in too low our determination of radiative lifetimes of the
a concentration. Again, the same considerations required the decay curves and E 3 P states of the TiO molecule (2). Briefly, a pulsed, supersonic to be acquired in a partial saturation regime of the absorption transitions, molecular beam of CrO molecules was generated by reaction of the species resulting in a 0.15 cm 01 linewidth FWHM. The spectra, which could be laser ablated from a Cr rod within the expansion of He carrier gas containing fitted with a rotational temperature of ca. 50 K, still exhibited R bandheads. 0.5% O 2 emitted by a fast pulsed valve. The molecular beam was collimated
The measurements were performed at the bandheads of the 5 P 01 R 5 P 01 to 4Њ full-width at half-maximum (FWHM) and was then crossed at right (R a and R b ), 5 P 0 R 5 P 0 (R b ), and 5 P 1 R 5 P 1 (R a and R b ) branches. The angles 110 mm after the ablation point with a pulsed, tunable dye-laser fluorescence decays were fitted to an exponential function using a leastbeam (0.1 cm 01 linewidth, 5 nsec pulse duration, 4 mm diameter). At this squares method (5). Estimate of the radiative lifetime was made with a point, the molecular beam pulse, with 2000 msec 0l velocity, had a FWHM higher limit of the fitting domain set to 90% of the maximum fluorescence temporal duration of 5 msec and a FWHM diameter of 6.5 mm. Ground intensity and a lower limit set to 2%. The higher limit was chosen very state CrO radicals were excited using the (B 5 P V R X 5 P V ) (0-0) transition conservatively to avoid taking into account data points acquired before near 605 nm (3, 4). The fluorescence of the (0-1) transition was isolated complete extinction of the laser light. The lower limit was chosen with through a SCHOTT RG630 filter and then detected by a photomutiplier tube (PMT) having a 2.5 nsec rise time (Hamamatsu R955). The PMT regard to signal-to-noise ratio considerations. All possible experimental