Ultraviolet photolysis of HS and its implications for SH radical production in the interstellar medium.

Hydrogen sulfide radicals in the ground state, SH(X), and hydrogen disulfide molecules, HS, are both detected in the interstellar medium, but the returned SH(X)/HS abundance ratios imply a depletion of the former relative to that predicted by current models (which assume that photon absorption by HS at energies below the ionization limit results in H + SH photoproducts). Here we report that translational spectroscopy measurements of the H atoms and S(D) atoms formed by photolysis of jet-cooled HS molecules at many wavelengths in the range 122 ≤ λ ≤155 nm offer a rationale for this apparent depletion; the quantum yield for forming SH(X) products, Γ, decreases from unity (at the longest excitation wavelengths) to zero at short wavelengths. Convoluting the wavelength dependences of Γ, the HS parent absorption and the interstellar radiation field implies that only ~26% of photoexcitation events result in SH(X) products.

State-to-state photodissociation dynamics of CO around 108 nm: the O(S) atom channel.

State-to-state photodissociation of carbon dioxide (CO2) via the 3p1Πu Rydberg state was investigated by the time-sliced velocity map ion imaging technique (TSVMI) using a tunable vacuum ultraviolet free electron laser (VUV FEL) source. Raw images of the O(1S) products resulting from the O(1S) + CO(X1Σ+) channel were acquired at the photolysis wavelengths between 107.37 and 108.

Photodissociation dynamics of HO and DO via the D[combining tilde](A) electronic state.

Photodissociation dynamics of HO and DO via the D[combining tilde] state by one-photon excitation have been investigated using the H/D atom Rydberg tagging time-of-flight technique. The TOF spectra of the H/D-atom product in both parallel and perpendicular polarizations have been measured. Product translational energy distributions and angular distributions have been derived from TOF spectra.

Vacuum ultraviolet photodissociation dynamics of CO near 133 nm: The spin-forbidden O(P) + CO(XΣ) channel.

Understanding vacuum ultraviolet (VUV) photodissociation dynamics of CO is of considerable importance in the study of atmospheric chemistry and planetary chemistry. Yet, photodissociation dynamics of the spin-forbidden O(P) + CO(XΣ) channel has not been clearly understood so far. Here, we study the O(P) + CO(XΣ) dissociation processes in the VUV photodissociation of CO at the photolysis wavelengths between 129.

Striking Isotopologue-Dependent Photodissociation Dynamics of Water Molecules: The Signature of an Accidental Resonance.

Investigations of the photofragmentation patterns of both light and heavy water at the state-to-state level are a prerequisite for any thorough understanding of chemical processing and isotope heterogeneity in the interstellar medium. Here we reveal dynamical features of the dissociation of water molecules following excitation to the (010) state using a tunable vacuum ultraviolet source in combination with the high-resolution H(D)-atom Rydberg tagging time-of-flight technique. The action spectra for forming H(D) atoms and the OH(OD) product state distributions resulting from excitation to the (010) states of HO and DO both show striking differences, which are attributable to the effects of an isotopologue-specific accidental resonance.

Vacuum ultraviolet photodissociation dynamics of NO via the CΠ state: The N(D) + NO(XΠ) product channels.

We study the vacuum ultraviolet photodissociation dynamics of NO via the CΠ state by using the time-sliced velocity map ion imaging technique. Images of N(D) products from the N atom elimination channels were acquired at a set of photolysis wavelengths from 142.55 to 148.