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

The electronic spectrum of germylidene (H2C=Ge), the simplest unsaturated g ermylene, has been observed for the first time. Jet-cooled H2CGe and D2CGe were produced by an electric discharge through tetramethylgermane diluted i n argon at the exit of a supersonic expansion. High-resolution spectra of ( H2CGe)-Ge-74 and (D2CGe)-Ge-74, obtained from (CH3)(4)Ge-74 prepared from i sotopically enriched Ge-74 metal, have been rotationally analyzed to yield the following r(0) structures: r(0)(')(CGe)=1.7908(2) Angstrom, r(0)(")(CH) =1.1022(5) Angstrom, theta(0)(')(HCH)=115.05(5)degrees, r(0)(')(CGe)=1.914( 4) Angstrom, r(0)(')(CH)=1.082(9) Angstrom, and theta(0)(')(HCH)=139.3(11)d egrees. The 367-354 nm (B) over tilde(1)B(2)-(X) over tilde (1)A(1) band sy stem consists of prominent perpendicular bands involving the CGe stretching (nu(3)) and CH2 scissors (nu(2)) vibrations and a weaker series of vibroni cally induced parallel bands involving the CH2 rocking mode (nu(6)). Vibron ic bands involving Delta v=2 changes in nu(6)(b(2)) and nu(4)(b(1)) have al so been assigned. The fluorescence decays of single rotational levels of th e 0(0)(0) band of (H2CGe)-Ge-74 exhibit molecular quantum beats for about 7 0% of the levels surveyed. Density of states arguments reveal that most of the beats originate from interactions with high rovibronic levels of the gr ound state. In one case, hyperfine splittings in the Fourier transform of t he beat pattern indicate an accidental coincidence with an excited triplet state level. The less frequent occurrence of quantum beats in germylidene c ompared to silylidene, where they are almost universal, can be attributed t o the smaller density of ground state levels at the zero-point energy of th e S-2 state in the former. (C) 1999 American Institute of Physics. [S0021-9 606(99)00826-0].