Photochemistry of HOSO radical in the gas phase

Abstract

The photochemistry of HOSO in the near-and deep-UV spectral range has been studied in the gas phase using the multireference configuration interaction MRCI+Q/aug-cc-pV(T+d)Z level of theory. HOSO is found to be a nonplanar radical in its ground electronic state with a torsion angle calculated to be 49.7 ○. The lowest three doublet electronic states are characterized by a large transition dipole moment and are implicated in the photodissociation of HOSO in the gas phase to generate SO and OH as products. Sulfur dioxide and hydrogen products may also result after UV absorption to reach the first excited state, and this channel competes with the production of OH and SO.

Spectroscopic Characterization of the First and Second Excited States of the HOSO Radical

“…Figure depicts these dihedral scans, with all other coordinates fixed at the MRCI+Q equilibrium geometry of that state. As Trabelsi et al previously reported, the X̃ 2 A state dihedral potential is characterized by a flat surface from 0° to ∼50°, with a steady increase in energy from 50° to 180°. The small gradient in this region causes the different electronic structure methods to converge to different dihedral angles.…”

“…This large difference between CCSD­(T) and MRCI is attributable to the flatness of the potential energy surface along the torsion angle. Trabelsi et al reported potential energy curves calculated along the torsional angle and found a flat potential, especially between 0° and 50° . Discussion surrounding the torsional potentials of all three states appears later in this section.…”

“…Ballester and Varandas calculated the ground state surface for the OH + SO → H + SO 2 reaction and found that only excited configurations of the HOSO radical are allowed to be formed . Recently, Trabelsi et al reported one-dimensional cuts of the potential energy surface of the HOSO radical along the stretching and bending coordinates and found that there exists the possibility of fluorescence after near-ultraviolet (UV) absorption . These studies indicate a void in the literature with a clear need for theoretical characterization of the lowest electronic states of the HOSO radical to help drive the laboratory detection of these states and elucidate its photochemical behavior and atmospheric and astronomical significance.…”

Successive Hydrogenation of SO and SO2 in Solid para-H2: Formation of Elusive Small Oxoacids of Sulfur

“…For instance, irradiating the samples with visible light (λ ≥ 360 nm) converts HSO 2 to HOSO, although HSO 2 also seems to dissociate to SO 2 and H (510 nm, red lines in Figures c and S2c–S4c in the Supporting Information). The reverse conversion can be achieved using shorter wavelengths (e.g., 270 nm, blue lines in Figures c and S2c–S4c in the Supporting Information), although this process competes with the photodissociation of HOSO to SO and OH (λ ≤ 330 nm). , It is worth recalling that the formed OH is unstable in para -H 2 and quickly converts to H 2 O (according to eq ). The photodissociation processes become so dominant at 240 nm that all SO 2 hydrogenation products decrease ubiquitously upon the irradiation at this wavelength (blue lines in Figures a and S2a–S4a in the Supporting Information).…”

“…The reverse conversion can be achieved using shorter wavelengths (e.g., 270 nm, blue lines in Figures 6c and S2c−S4c in the Supporting Information), although this process competes with the photodissociation of HOSO to SO and OH (λ ≤ 330 nm). 107,146 It is worth recalling that the formed OH is unstable in para-H 2 and quickly converts to H 2 O (according to eq 5).…”