Microwave spectrum of silylidene H2CSi

Abstract

Rotational spectral lines of the H2CSi molecule are observed in the millimeter-wave and submillimeter-wave regions. The molecule is produced in a glow-discharge plasma of a gaseous mixture of SiH4 and CO. Rotational constants and centrifugal distortion constants have precisely been determined from observed frequencies of 32 a-type transitions with J=5–4 to J=12–11 and Ka=0 to Ka=4. From the observed inertial defect, the vibrational frequency of the CH2 rocking mode is estimated to be as low as 331 cm−1, which is consistent with the large quartic centrifugal distortion constants, DJK and d2. Higher-order centrifugal distortion constants up to the octic terms are necessary to obtain a good fit between the observed and calculated frequencies within experimental uncertainties. The low vibrational frequency and the necessity of the higher-order centrifugal distortion terms indicate a floppy nature of the CH2 rocking mode. A preliminary radioastronomical search for H2CSi in space has been carried out toward a few astronomical sources without success.

The Rotational Spectra of H2CCSi and H2C4Si

“…0|L g |n 2 E n − E 0 + effects of nuclear charges, [3] where g = a, b, c. The contribution to Eq. [3] from the rotation of the nuclear frame of the molecule is readily calculated from the molecular structure.…”

“…[3] from the rotation of the nuclear frame of the molecule is readily calculated from the molecular structure. For H 2 CCSi it is of order 10 kHz or less, and can be neglected in the present analysis.…”

“…Although silicon analogs of many pure carbon clusters (C n ) and acetylenic free radicals (C n H) have recently been characterized by high-resolution spectroscopy (1,2), only H 2 CSi, the silicon analog of vinylidene (H 2 CC:), has been reported in the gas phase (3,4). Because small silicon-bearing molecules such as SiS, SiC, and SiC 2 , and the cumulene carbenes H 2 C 3 (5), H 2 C 4 (6), and H 2 C 6 (7) are abundant in the circumstellar shells of evolved carbon stars (8), H 2 CCSi and longer silacumulenes are plausible candidates for astronomical detection.…”

Ab initio Study of Mechanism of Cycloaddition Reaction between Germylene Silylene (H2GeSi:) and Acetone

“…From the potential energy profile of the cycloaddition reaction between singlet state germylene silylene and acetone with CCSD(T)/6-31G*//MP2/6-31G* method, it can be predicted that the dominant reaction channels of the cycloadditional reaction between singlet state germylene silylene and acetone are reaction (4) and reaction (5). The process of the reaction (4) consists of two steps, and the main product is a distorted fourmembered ring product (P4).…”

“…Some of the ground-state vibrational frequencies of H 2 C＝Si and D 2 C＝Si have been reported 4 to have been obtained by Bengali and Leopold using photoelectron techniques. Most recently, Izuha et al 5 have obtained the microwave spectrum of H 2 C＝Si in a glow-discharge plasma of a mixture of SiH 4 and CO. Theoretical study indicates that the ground state of H 2 C＝Si is singlet state.…”