Theoretical study of the spectroscopy and radiative transition probabilities of Si2 from visible to infrared

• Published in: Physical chemistry chemical physics : PCCP Vol. 25; no. 41; pp. 28350 - 28362
• Main Authors: Xiao, Lidan, Yang, Yun, Li, Xinyu, Minaev, Boris F, Yan, Bing
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 25.10.2023
• Subjects: Configuration interaction; Electron states; Mathematical analysis; Oscillator strengths; Oscillators; Radiative lifetime; Spectrum analysis; Spontaneous emission; Transition probabilities
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/d3cp02512h

High level ab initio calculations on the electronic states of a silicon dimer (Si2) have been carried out by employing a multi-reference configuration interaction plus Davidson correction (MRCI + Q) approach with the aug-cc-pVQZ basis set. The scalar relativistic correction is taken into consideration by the second-order Douglas–Kroll–Hess approximation. In the present work, the transition properties (oscillator strength, Einstein spontaneous emission coefficient and radiative lifetime) of the singlet–singlet, triplet–triplet, and quintet–quintet transitions of Si2 are discussed. We emphasize the triplet–triplet emission bands H3Σu−–X3Σg−, K3Σu−–X3Σg− and D3Πu–L3Πg which are dominant for 0–11 (18 822 cm−1), 0–0 (30 672 cm−1), and 0–0 (28 881 cm−1) transitions, respectively. In addition, the strong experimentally observed b1Πu–d1Σg+ band around 4184 cm−1 corresponds to the second 1Σg+–b1Πu combination in the infrared region. The calculated oscillator strengths of the singlet–singlet transitions (f1Πg–e1Σu−, 21Πg–b1Πu, b1Πu–d1Σg+ and g1Δu–a1Δg) are in the order of 10−3. From a theoretical point of view, the 0–0 sub-band for the f1Πg–e1Σu− transition, 0–7 for 21Πg–b1Πu, 0–0 for b1Πu–d1Σg+ and the 0–7 vibronic bands for the g1Δu–a1Δg transition may be observed experimentally. It is expected that the present results could provide theoretical support for a deeper understanding of the experimental Si2 spectra providing further applications in astrophysics.