Overview of the transient response of HONO after selectively pumping the (a) trans and the (b) cis species. The labeled arrows mark certain features discussed in the text.
(a) Transient spectra of 0.6, 1.8, 3.2, 10, and , respectively, after pumping trans-HONO, focused into the trans band. Cooling cascades through one mode (presumably ) with four to zero quanta (see labels) of that mode excited. (b) Time scans at selected frequency positions corresponding to four to zero quanta (see labels) of that mode. (c) and (d) The same when pumping cis-HONO. The trans photoproduct relaxes through the same cooling cascade as when pumping trans directly. The trace with four quanta is omitted since signal-noise is insufficient to resolve it.
Solid line: time dependence of the weak band at marked by a white arrow in Fig. 1(a), in comparison with the time dependence of the excited state absorption (, dotted line). The latter is down scaled by a factor of 53. The data are taken from Ref. 24.
(a) Integrated intensity of the trans photoproduct band after selective excitation of cis-HONO and (b) the kinetics of the negative bleach/stimulated emission band of cis-HONO. The plot combines data from our previous publication (, open squares) (Ref. 24) with that of the present work (, black squares).
Transient spectra used to estimate (a) the quantum yield and (b) the quantum yield. The delay time positions are chosen such that either the OH stretch vibration has just relaxed, but the bleach part is still present (gray lines, in the case of trans-HONO and in the case of cis-HONO), or such that the energy has dissipated essentially completely out of the molecule (black lines, in both cases). The spectrum in (a) is scaled by a factor of 2 for better visibility.
Dependence of the photoequilibrium constant on temperature (squares, left scale), and that of the ratio of integrated cross sections of the OH stretch absorption bands (circles right scale). The insert shows a cis-trans difference spectrum at measured under continuous irradiation in a FTIR spectrometer.
Kinetic scheme to describe the two-step isomerization process.
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