Theoretical Investigation of the Structure and Vibrational Spectrum of the Electronic Ground State X̃(¹A‘) of HSiCl

Abstract

The transient HSiCl (monochlorosilylene) is a species for which structure and spectroscopic properties are almost unexplored by quantum chemical methods. In this work, CCSD and CCSD(T) methods in conjunction with Dunning's hierarchy of basis sets are used to investigate both aspects of this biradical. The CCSD(T)/ cc-pCVTZ method using analytical second derivatives of the energy in combination with second order perturbation theory to evaluate the anharmonicity shows to be an efficient strategy to calculate its fundamental vibrational frequencies. Especially remarkable for its anharmonic nature is the calculated value for ν 1 (Si-H stretching) which is only 4 cm -1 bellow than the observed transition. The experimental structure is investigated by analyzing the experimental rotational constants. This latter goal was accomplished reporting high-level ab initio r e -structures as well as empirical structural parameters using CCSD(T)/cc-pCVTZ vibrational corrections of the experimental rotational constants.

Hyperfine Interactions in HSiCl

“…The frequencies of the hyperfine components of the J ) 1-0 transition (whose energy is approximately B + C) are equally sensitive to the value of the spin rotation constants C bb (Cl) and C cc (Cl) but insensitive to the value of C aa (Cl). The value for C bb ( 35 Cl) in H 28 Si 35 Cl given in Table 2 as 5.2 (7) kHz is based on (arbitrarily) setting C cc ( 35 Cl) equal to zero. If, in eq 1 for the hyperfine Hamiltonian, we were to substitute the scalar interaction, C I (Cl)[I a J a + I b J b + I c J c ], for C bb (Cl)I bb J bb , then the value of C I (Cl) would be exactly 1 / 2 of the value we report for C bb (Cl).…”

“…There is a new version of the Gaussian program under development which currently can calculate the spectroscopic hyperfine constants for singlet states (χ and C, the nuclear quadrupole coupling, and nuclear spin-rotation interaction tensors) along with the more complete set of fine and hyperfine constants for doublet radicals (E, a F , T; electron spin-rotation, Fermi contact, and nuclear spin-electron spin interactions). 33 Using this program, we calculate for the chlorine nucleus in H 28 Si 35 Cl C aa ) 131 kHz, C bb ) 5.7 kHz (experimental, 5.2 (7) kHz with C cc assumed zero), and C cc ) 0.04 kHz; we calculate for the silicon nucleus in H 29 Si 35 Cl C aa ) -485 kHz, C bb ) -7.9 kHz, and C cc ) -5.0 kHz. Our experimental value for C bb ( 29 Si) is -15(2) kHz with C cc assumed to be zero which should be compared with the sum of the calculated values for the bb and cc components of the tensor which is -13 kHz.…”

“…6 Recently, a high-level ab initio calculation using the CCSD(T) method has been performed in which the experimental structure and the vibrational frequencies are well reproduced. 7 The current work is the first pure rotational spectroscopy of monochlorosilylene. The ∼1 kHz resolution in the current experiment, compared to the ∼30 MHz resolution of the electronic spectroscopy, allows us to measure an improved effective rotational constant and to measure the nuclear quadrupole and nuclear spin-rotation hyperfine structure of HSiCl for the first time.…”

New ab initio potential energy surfaces for both the ground (X̃1A′) and excited (Ã1A″) electronic states of HSiCl and the absorption and emission spectra of HSiCl/DSiCl

“…On the other hand, only a few theoretical studies have been reported for monohalosilylenes 10–15. Among these studies, Vazquez et al12 performed a theoretical investigation of the structure and vibrational spectrum of the electronic ground state $ \tilde X^1 A' $ of HSiCl using the coupled cluster singles and doubles with perturbative triples method [CCSD(T)] with cc‐pVTZ basis set. Mok et al13 carried out the Frank‐Condon simulation emission spectra of HSiF/DSiF including anharmonicity in 2004.…”

Anharmonic spectra of methanol and silanol: A comparative study

“…In a recent anharmonic theoretical work on HSiCl molecular species at the CCSD(T)/cc-pVTZ level [56], the harmonic and anharmonic frequencies obtained for the Si-H stretching are 2049 and 1972 cm À1 , respectively. This difference of 77 cm À1 is in accordance with the differences yielded by the cc-VSCF method, i.e., 99 cm À1 (m 2 ), 87 cm À1 (m 3 ), and 102 cm À1 (m 9 ).…”