  The mass difference of the nuclides 180W and 180Hf has been measured with the
Penning-trap mass spectrometer SHIPTRAP to investigate 180W as a possible
candidate for the search for neutrinoless doubleelectron capture. The Q-value
was measured to 143.20(27)keV. This value in combination with the calculations
of the atomic electron wave functions and other parameters results in a
half-life of the 0+ \rightarrow 0+ ground-state to ground-state double-electron
capture transition of approximately 5\cdot10E27 years/<m_ee[eV]>^2.
