The electronic spectrum of germanium methylidyne (GeCH), the prototypical organogermanium compound

The (A) over tilde (2)Sigma(+)-(X) over tilde (2)Pi(i) electronic transitio n of jet-cooled germanium methylidyne has been recorded in the 730-555 nm r egion by laser-induced fluorescence techniques. The radical was produced in a pulsed electric discharge using tetramethylgermane as the precursor. The band system consists of perpendicular and vibronically induced parallel ba nds with upper state frequencies of nu(2)'=638/497 cm(-1) and nu(3)'=990/95 2 cm(-1) for GeCH/GeCD. The (2)Sigma(+)-(2)Pi(3/2) components of the 0(0)(0 ) bands of GeCH and GeCD and the 2(0)(1) band of GeCH have been recorded wi th sufficient resolution to assign the transitions of the Ge-70, Ge-72, Ge- 74, and Ge-76 isotopomers. The rotational constants of the various hydrogen and germanium isotopomers were used to derive the following molecular stru ctures: r(0)"(Ge-C)=1.775 79(21) Angstrom, r(0)"(C-H)=1.0673(12) Angstrom, r(0)'(Ge- C)=1.673 66(8) Angstrom, and r(0)'(C-H)=1.0589(5) Angstrom. The g round state germanium-carbon bond length is typical for a Ge=C double bond, but in the excited state it corresponds to a triple bond. This is a conseq uence of promotion of an electron from a nonbonding sigma orbital to a pi b onding orbital to form the ...sigma(1)pi(4)((2)Sigma(+)) excited state. In this study we provide the first experimental value for the length of the ge rmanium-carbon triple bond. (C) 2000 American Institute of Physics. [S0021- 9606(00)01619-6].