Optical Spectrum and Photochemistry of Si2O2+
Year: 2025
Type: article
Abstract: Silicates and silica are the major components ofinterstellar silicon-based dust grains and mainly composed of siliconand oxygen. Information about their geometric, electronic, optical, andphotochemical properties is crucial for developing astrochemical modelsdescribing dust grain formation. To this end, we characterize herein theoptical spectrum of mass-selected Si2O2+ cations in the 295−709 nmrange using electronic photodissociation (EPD). The EPD spectra arerecorded in a quadrupole/time-of-flight tandem mass spectrometercoupled to a laser vaporization source and compared to complementarytime-dependent density functional theory (TD-DFT) calculations at theUB3LYP-D3/aug-cc-pVQZ level of theory, determining structures,energies, electronic spectra, and fragmentation energies of the low-energy isomers. The EPD spectrum is observed in the lowest-energy fragmentation channel, corresponding to SiO+ + SiO. The highcalculated dissociation threshold of D0 = 4.60 eV (37,102 cm−1) requires two-photon absorption for EPD. The three electronictransitions observed at 19,264, 25,667, and 32,216 cm−1 are attributed to transitions from the doublet ground state of the most stablerhombic structure of Si2O2+ (D2h, 2B1u) into the first, fourth, and fifth excited doublet states, D1(2Ag), D4(2B2g), and D5(2B3u),respectively. The resolved vibronic structure of the D4 and D5 state is analyzed by Franck−Condon Herzberg−Teller (FCHT)simulations to suggest vibrational assignments. The calculations indicate the reduction of symmetry from D2h to C2v in the D4 statealong the ν4(b1u) coordinate (resulting in a flat double minimum potential), while the dipole-forbidden D5 state gains its vibronicintensity from HT coupling to the same ν4 mode.
Source: DepositOnce
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W6923566183
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