Single vibronic level emission spectra have been obtained by pumping individual vibronic bands in the (B) over tilde (1) B-2-(X) over tilde (1)A(1) electronic transitions of jet-cooled H2CGe and D2CGe. Analysis of the spectra gave for the first time the frequencies of the following ground state fundamentals: for H2CGe, nu(2) = 1238 cm(-1), nu(3)=782 cm(-1), nu(4)=673 cm(-1) nu(6)=351 cm(-1), and for D2CGe, nu(1)=2089 cm(-1), nu(2)=1000 cm(-1), nu(3) = 694 cm(-1), nu(4) = 520 cm(-1), and nu(6) = 282 cm(-1). The vibrational data have been combined with our previously determined molecular structures to obtain approximate harmonic force fields for the ground and excited states. Franck-Condon simulations of the emission spectra in the harmonic approximation show reasonable agreement with experiment, except for unexpected activity in the out-of-plane bending mode. This is attributed to a very anharmonic out-of-plane bending potential in the S-2 excited state. Germylidene also has a very low ground state CH2 rocking frequency (nu(6)) which is along the normal coordinate leading to isomerization to the less stable trans-bent germyne isomer, H-C=Ge-H.