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20
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84951891990
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The dye laser system has been described previously by Lehmann, Scherer, and Klemperer (Ref. 21), but here the laser cavity was not extended and its free spectral range was [formula omitted] We have also implemented single-mode operation and continuous scanning by locking the cavity mode to the air spaced étalon with an integral control feedback loop (see, e.g., Ref. 22)
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23
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85038136951
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At the high sensitivities used for these measurements there were numerous transitions of uncomplexed [formula omitted] which saturated our lock-in amplifier. The fluorescence excitation continuum level dropped significantly when Ar was removed from the expansion, but the highest signal level recorded for the stronger [formula omitted] transitions stayed the same, i.e., at the saturation level of the lock-in. The [formula omitted] signal levels relative to the continuum level were thus higher when the continuum was lower, i.e., in the reference scans without Ar in the expansion. When subtracting the reference from the scan with Ar there is thus a large negative signal for these [formula omitted] transitions relative to the continuum level
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24
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84951893690
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The glass cutoff filters (CVI) have a transmittance of 0.5 at the nominal cutoff wavelength. The transmittance is a fairly sharp function of wavelength; it falls to [formula omitted] at 15 nm to the blue and rises to [formula omitted] at 20 nm to the red of the.nominal cutoff
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25
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84951892309
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We have seen no evidence for saturation of the continuum or of the discrete bands of [formula omitted] and [formula omitted] i.e., the signals appear to be perfectly linear with respect to laser power. Relative intensities should thus be a good measure of relative populations
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26
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84951885988
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The maximum quantum efficiency for collision-induced generation of fluorescence from continuum excitation is taken as the product of the [formula omitted] collision rate and the dissociation time for [formula omitted] on the [formula omitted] potential. Using the [formula omitted] potential curve of Chapman and Bunker (Ref. 27) [which was originally misassigned as the [formula omitted] potential], we have estimated a dissociation time of [formula omitted] This is the transit time for lengthening of the I–I bond from its value at the repulsive wall following 543 nm excitation to the bond length of the outer classical turning point of the B state at the same energy, [formula omitted] (Ref. 28). A very conservative estimate for the frequency at which an [formula omitted] molecule collides with Ar atoms in our He expansion was determined using the Ar gas density and velocity at the nozzle. In addition, a rather large collision cross section, based on van der Waals diameters, of [formula omitted] was used. The resulting frequency of collision with Ar for each [formula omitted] molecule is [formula omitted] The maximum quantum efficiency for collisionally induced fluorescence is thus [formula omitted]
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34
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85038135225
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[formula omitted] bands of the linear isomer will overlap when dispersed over the continuum. Since the intensities of individual bands should vary smoothly will [formula omitted] the effective intensity based on a single [formula omitted] either integral or nonintegral, is adequate
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