The electronic spectrum, molecular structure, and oscillatory fluorescence decay of jet-cooled germylidene (H2C=74Ge), the simplest unsaturated germylene

Abstract

The electronic spectrum of germylidene (H2C=Ge), the simplest unsaturated germylene, has been observed for the first time. Jet-cooled H2CGe and D2CGe were produced by an electric discharge through tetramethylgermane diluted in argon at the exit of a supersonic expansion. High-resolution spectra of H2C74Ge and D2C74Ge, obtained from (CH3)474Ge prepared from isotopically enriched 74Ge metal, have been rotationally analyzed to yield the following r0 structures: r0″(CGe)=1.7908(2) Å, r0″(CH)=1.1022(5) Å, θ0″(HCH)=115.05(5)°, r0′(CGe)=1.914(4) Å, r0′(CH)=1.082(9) Å, and θ0′(HCH)=139.3(11)°. The 367–354 nm B̃1B2–X̃ 1A1 band system consists of prominent perpendicular bands involving the CGe stretching (ν3) and CH2 scissors (ν2) vibrations and a weaker series of vibronically induced parallel bands involving the CH2 rocking mode (ν6). Vibronic bands involving Δv=2 changes in ν6(b2) and ν4(b1) have also been assigned. The fluorescence decays of single rotational levels of the 000 band of H2C74Ge exhibit molecular quantum beats for about 70% of the levels surveyed. Density of states arguments reveal that most of the beats originate from interactions with high rovibronic levels of the ground state. In one case, hyperfine splittings in the Fourier transform of the beat pattern indicate an accidental coincidence with an excited triplet state level. The less frequent occurrence of quantum beats in germylidene compared to silylidene, where they are almost universal, can be attributed to the smaller density of ground state levels at the zero-point energy of the S2 state in the former.

Rotationally Resolved LIF Spectra of the A2Σ+–X2Πr Transition of Jet-Cooled 74Ge35Cl

“…High-resolution (0.04 cm −1 ) spectra of 74 GeCl were recorded using an isotopically enriched 74 GeCl 4 precursor, which was cooled to −25 • C to preserve the sample. The 74 GeCl 4 was synthesized by heating 74 Ge metal (Isoflex, 99.7%) in a closed system pressurized with 20 psi of Cl 2 (Aldrich) (15). The excitation laser was an excimer pumped Lambda Physik FL3002E dye laser equipped with an angletuned intracavityétalon.…”

“…Germanium monochloride was produced using the discharge jet technique described in more detail elsewhere (15). Briefly, the room temperature vapor of germanium tetrachloride (Aldrich) was seeded in 30 psi of argon and expanded through a pulsed valve (General Valve, Series 9) into a cylindrical discharge channel.…”

Heavy atom nitroxyl radicals. II: Spectroscopic detection of H2As=O, the prototypical arsenyl free radical

“…Well-known examples of molecules that exhibit anomalous fluorescence in violation of Kasha's rule include azulene and several of the thiocarbonyl compounds ͑XYC= S͒. 34 More recently, we have discovered 35,36 that H 2 C = Si and H 2 CGe also fluoresce from the B 1 B 2 excited state, with a variety of interesting photophysical properties, including single rotational level fluorescence decays that exhibit molecular quantum beats. The occurrence of anomalous emission from all these molecules is attributable to their unique energy level structure in which the second excited electronic state is far removed from the first, so that coupling between the two excited states is minimal.…”

Ab initio Study of Mechanism of Forming a Germanic Hetero‐Polycyclic Compound between Germylidene (H2C=Ge:) and Acetone

“…In 1997, Clouthier et al 1 from University of Kentucky observed the first unsaturated germylene-germylidene, which is produced by striking an electric discharge in a high-pressure argon pulse using the tetramethylgermane (TMG) vapor as the precursor. They obtained its molecular structure and the ab initio predictions, 2 electronic spectrum 2 and oscillatory fluorescence decay 2 of jet-cooled germylidene (H 2 C＝ Ge:), and learnt the ground state 3 of H 2 C＝Ge: and D 2 C ＝Ge:, the stimulated emission pumping (SEP) spectroscopy 4 of the first excited singlet state of germylidene. Stogner and Grev 5 have published the extensive ab initio calculations on both germylidene and the trans-bent germyne HC≡GeH isomer.…”