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Photodissociation of in the state: A slice imaging study and reinterpretation of previous results
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Image of FIG. 1.
FIG. 1.

Peak internal energy of the fragments produced in coincidence with for two different dissociation channels (high and low internal energies) at different excess energies in the state. The figure compares previous studies; McFarlene et al. (Ref. 33), Ahmed et al. (1) (Ref. 34), Brouard et al. (Ref. 16), Ahmed et al. (2) (Ref. 39), Coroiu et al. (Ref. 41), and Hancock and Morrison (Ref. 25); with this work. The error bars represent the half width half maximum of the internal energy distributions reported in these studies. In the experiments of Hancock and Morrison (Ref. 25) only vibrational profiles were recorded. In this case the rotational energy corresponding to has been added to the most probable vibrational energy for the low internal energy channel (to give a total internal energy of ). This point is drawn as a filled triangle. The lines drawn through the points are quadratic least-squares fits but are merely a guide to the eye and have no physical significance. The solid line links data for the channel producing fast O atoms. The dashed line links data for the channel producing slow O atoms.

Image of FIG. 2.
FIG. 2.

dc slice velocity map images of the (a) , (b) , and (c) fragments recorded using a single laser for both photolysis of the parent molecule and photoionization of the O fragment. The laser, which is polarized vertically to the image plane, is scanned over approximately 0.016 nm around each ionization resonance in order to ensure that the entire Doppler profile of the O fragments is evenly sampled. Each image is recorded for laser shots. Panel (d) shows the translational energy distribution produced from the photodissociation of via the state with associated peak labels as discussed in the text. The distribution is simply obtained by angular integration of the corresponding image (a), multiplication by the appropriate Jacobian, , and calibrated against a known kinetic energy release spectrum, usually of O atoms from the photodissociation of , recorded immediately prior or post the image acquisition with exactly the same extraction voltages and laser/molecular beam intersection point. Panels (e) and (f) show the photofragment distributions as in (d) but for the and fragments, respectively.

Image of FIG. 3.
FIG. 3.

Panel (a) mass-resolved (TOF) REMPI excitation spectrum of recorded at single photon excitation energies spanning the range of the (2,3) transition. Peak separations are noted to be around 4.6 meV. The expected position of the (2,3) band head is superimposed on the spectrum as a dashed vertical line at . The lines in the spectrum marked (a)–(c) correspond to the excitation energies used to record the images presented in Fig. 4. Panels (b) and (c) show simulated NO absorption spectra for the NO transition using the LIFBASE spectral simulation software package (Ref. 50). Panel (b) shows the absorption of NO fragments produced in with a peak in a statistical rotational distribution at , while (c) shows the absorption of NO fragments produced in with a sharp rotational profile peaking at with a FWHM corresponding to the energy spread of ten rotational levels.

Image of FIG. 4.
FIG. 4.

Representative velocity map images and corresponding kinetic energy release spectra of NO fragments formed at excitation energies close to 230 nm [(a)–(c) in Fig. 3]. The kinetic energy release of these fragments is too high for the fragments to be rotationally hot radicals in . These NO fragments must be in the 2, 1, or 0 vibrational states. See text for discussion.

Image of FIG. 5.
FIG. 5.

energy release spectra recorded at a backing pressure of 1 bar and nozzle temperatures of 295 K (dotted line), 345 K (dashed line), and 393 K (solid line).

Image of FIG. 6.
FIG. 6.

and translational anisotropies as a function of the kinetic energy release.


Generic image for table
Table I.

Transition probabilities and excitation energies for selected vibrational bands in the absorption spectrum of NO. The data are taken from constants published in the LIFBASE spectral simulation program (Ref. 50).

Generic image for table
Table II.

Vibrational and rotational assignments of the NO cofragment responsible for the peaks occurring in the kinetic energy release spectrum [Fig. 2(d)].

Generic image for table
Table III.

As Table II but for the kinetic energy release spectrum [Fig. 2(f)].


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Photodissociation of NO2 in the (2)B22 state: A slice imaging study and reinterpretation of previous results