Shape Resonances in H2 as Photolysis Reaction Intermediates

Abstract

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The vibronic state dependent predissociation of H2S: determination of all fragmentation processes

“…A small fraction shows a completely different energy disposal, however, involving minimal vibration excitation ( v ′′ mp = 0, 1) and a highly inverted rotational population distribution that appears to peak at the highest J ′′ value permitted by energy conservation. The finding of highly rovibrationally excited H 2 fragments accords with the conclusions of a previous one colour resonance enhanced multiphoton ionization (REMPI) study of the H 2 fragments formed when exciting H 2 S (using two-photons) to similar total energies, 54 and we note that Ubachs and co-workers 55–57 have recently exploited similar two-photon excitations of H 2 S as a source for high resolution spectroscopy studies of highly excited rovibrational levels of H 2 .…”

“…A small fraction shows a completely different energy disposal, however, involving minimal vibration excitation (v ′′ mp = 0, 1) and a highly inverted rotational population distribution that appears to peak at the highest J ′′ value permitted by energy conservation. The nding of highly rovibrationally excited H 2 fragments accords with the conclusions of a previous one colour resonance enhanced multiphoton ionization (REMPI) study of the H 2 fragments formed when exciting H 2 S (using two-photons) to similar total energies,54 and we note that Ubachs and coworkers[55][56][57] have recently exploited similar two-photon excitations of H 2 S as a source for high resolution spectroscopy studies of highly excited rovibrational levels of H 2 .The simulations of the P(E T ) distributions obtained at l = 146.50 and 139.11 nm (Fig.S9 †) return similar bimodal H 2 product state population distributions but, even by l = 140.96 nm (Fig.S8(a) †), the rival three-body channel (4) is starting to contribute to the measured S( 1 D) images. This introduces further uncertainty in simulating the P(E T ) spectra, and the best-t simulation shown for l = 125.05 nm (Fig.S9 †) is guided by assuming two contributing energy disposals in the S( 1 D) + H 2 (v ′′ , J ′′ ) products as at longer excitation wavelengths.…”

“…52,53 Similar trends persist at all shorter photolysis wavelengths, as illustrated by the P(E T ) data recorded at  = 122.95 nm (Fig. 2(d fragments formed when exciting H 2 S (using two-photons) to similar total energies 54 , and we note that Ubachs and co-workers [55][56][57] have recently exploited similar two-photon excitations of (c) Imaging S( 1 S) photoproducts. Estimating the quantum yields of fragmentation channels probed in different PTS experiments is complicated by hard to define detection efficiencies, but the current knowledge suggests that the S( 1 S) + H 2 yield is lower than that for S( 1 D) + H 2 products.…”

Precision measurement of quasi-bound resonances in H$_2$ and the H + H scattering length

“…The present study, of which a preliminary report was published previously [46], explores the energy range just above the dissociation threshold of H 2 upon two-photon UV-photolysis of hydrogen sulfide molecules. This results in the detection of quasi-bound states in H 2 , using 2+1' resonance-enhanced multi-photon ionization, and in the accurate determination of the excitation energies of the long-lived resonances.…”

The quasi bound spectrum of H 2

“…It is worth mentioning at this point that the Ubachs group in Amsterdam has been able to probe some of these highly excited rotational quasibound levels thanks to a new experimental setup involving three VUV lasers [11,12] , where highly rotationally excited H 2 is produced from the photodissociation of H 2 S induced by a 2-photon absorption experiment. These studies beautifully confirm the energy level positions of H 2 derived from the theoretical computations of the ground state electronic potential of H 2 by Czachorowski et al [13].…”