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Site-dependent photodissociation of vibronically excited molecules
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Image of FIG. 1.
FIG. 1.

(a) D (magenta) and (b) H (cyan) photofragment electronic action spectra, obtained due to dissociation, and (c) absorption (red) and (d) R2PI (orange) spectra of . The black lines in each trace are the corresponding simulated spectra, obtained from multiple Lorentzians. The assignment of the observed bands, based on Ref. 6(c), appears at the top of the figure.

Image of FIG. 2.
FIG. 2.

The yield of the D (magenta) and H (cyan) photofragments resulting from dissociation and its ionization efficacy (orange) as a function of excitation energy. The D, H, and R2PI spectra were normalized relative to the signal of the feature corresponding to the band origin. The black line exhibits the transmission coefficient for tunneling of H atoms in cleavage of the N–H bond of methylamine, as a function of excitation energy [Ref. 15(e)]. This line exhibits the -shaped curve that was obtained due to the fit of the hyperbolic cosine potential to the calculated N–H PES [Ref. 15(e)], and the experimental data are displayed as squares.

Image of FIG. 3.
FIG. 3.

(a) H (solid circles) and (b) D (circles) Doppler broadened profiles obtained due to approximate photodissociation of excited to the (A) and (B) states on the electronic state. The solid lines represent the Gaussians fitted to the measured profiles and the insets represent the respective Maxwellian translational energy distributions extracted from them. The arrows in (a) and (b) mark the maximum available energies for H and D, respectively, for dissociation of through the electronic state.

Image of FIG. 4.
FIG. 4.

Schematics of two possible predissociation processes that could lead to C–D bond cleavage in . Molecules that were directly photoexcited to specific vibronic state on the PES (vertical arrow) evolve to a “hot” state on the ground PES through (a) radiationless transition via internal conversion (magenta arrow) and (b) tunneling through the barrier on the N–H PES, while evolving toward the ground state potential (magenta arrow) and eventually bouncing back to the CI and passing through it (orange arrow).


Generic image for table
Table I.

Energies for excitation of methylamine- to specific vibrational states on the first excited electronic state, , assignment of these states, H/D ratios resulting through N–H and C–D bond fissions and average translational energies of the H and D photofragments.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Site-dependent photodissociation of vibronically excited CD3NH2 molecules