Harmonic Two-Phonon γ-Vibrational State in Neutron-Rich<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow/><mml:mrow><mml:mn>106</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math>Mo

The neutron-rich ${}^{106}$Mo nucleus has been studied by prompt \ensuremath{\gamma}-ray spectroscopy following the spontaneous fission of ${}^{248}$Cm. The characteristics of the rotational band built on a state at 1435 keV identifies the band head as the best candidate for a harmonic double-phonon ${K}^{\ensuremath{\pi}}{\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}4}^{+}$ \ensuremath{\gamma}-vibrational state observed so far.