Absorption spectroscopy of SiH2 near 640 nm

Abstract

The à 1 B 1 -X 1 A 1 absorption spectrum of SiH 2 has been observed using intracavity laser absorption spectroscopy with an equivalent path length of up to 13.0 km and the à 1 B 1 (0, 0, 0)-X 1 A 1 (0, 0, 0) band near 640 nm recorded for the first time. The silylene radical was generated in a continuous discharge in a flowing mixture of silane in argon, giving a concentration of the order of 10 10 SiH 2 /cm 3 . The spectrum spans the region between 15350 and 16100 cm Ϫ1 . Rotational transitions have been assigned to levels up to Jϭ16 and K a ϭ9, with ⌬K a up to 5, ⌬K c up to 4. Perturbations have been detected in the spectrum, due to Renner-Teller and spin-orbit interactions between both electronic states and the 3 B 1 state, predicted to be between them. However, the strength of the irregular perturbations affecting the rotational states of à 1 B 1 ͑0,0,0͒ state is found to be much weaker than that affecting the other (0, v 2 Ј, 0) levels previously studied. The analysis of the spectrum has allowed the determination of the rotational constants of the 1 B 1 ͑0,0,0͒ level, and a new estimation of those of the vibrational and electronic ground state. The geometry of the excited electronic level has also been determined for the first time from accurate experimental data. A change in the structure of this molecule takes place with this transition, the equilibrium angle opening from 92°to 122.4°, while the bond distance is reduced from 1.51 to 1.485 Å.

Singlet-triplet gaps in diradicals by the spin-flip approach: A benchmark study

“…These diradicals are popular as benchmark systems, [33][34][35][36][37][38][39]41,60 because of their small size ͑but rich electronic structure͒, and the availability of experimental data. [61][62][63][64][65][66] For these systems, we compare the performance of the SF models against a variety of single-and multireference methods, and investigate the convergence of different methods with respect to the one-particle basis set. Next we consider a set of diatomic molecules with a diradical singlet state ͑NH, NF, OH ϩ , and O 2 ͒ for which accurate experimental data are available.…”

Detection and characterization of singly deuterated silylene, SiHD, via optical spectroscopy

“…The most obvious explanation for the observed bi-exponential behavior is that two or more different transitions were simultaneously excited due to a blending of lines. 14 The LIF excitation data set for SiHD (Table I) is less extensive than the data sets associated with the previous visible 25 or infrared 26 absorption spectra of SiH 2 due mainly to the small fluorescence quantum yield for the higher rotational levels of theà 1 A ′′ state. Accordingly, the spectroscopic parameters for SiHD are somewhat less well determined than those for SiH 2 .…”

“…Initial assignment of the c-type transitions in the excitation spectrum was readily accomplished by predicting the spectrum using estimated rotational parameters based upon the previously determined structure 25 of SiH 2 . Combination/differences revealed that the energies were not severely perturbed.…”

“…In the case of theà 1 B 1 state, they were derived from the analysis of cwintracavity laser absorption and cw-cavity ring down spectrum of the 0 0 0 and 2 2 0X 1 A 1 →à 1 B 1 bands. 24,25 In those studies, rotational information up to J = 16, K a = 9 was obtained from the analysis of Doppler limited spectra. A combined fit with the previous visible 7,8 and infrared 17 absorption measurements was performed.…”

The high-temperature rotation-vibration spectrum and rotational clustering of silylene (SiH2)

“…3. The first excited triplet state (ã 3 B 1 ) of SiH 2 is around 7000 cm −1 [54] while the first excited singlet state (Ã 1 B 1 ) lies at 15 500 cm −1 [55]. The presence of these states would have had an effect on the accuracy of the computed ab initio PES and DMS, due to Renner-Teller and spin-orbit interactions between these electronic states, which were not taken into account here.…”