= Solution
\b[The 375 meV pair should shift most fractionally, towards zero bias], because C–H stretching has strong <hydrogen> displacement. A reduced-mass estimate gives
$$
\frac{\omega_{CD}}{\omega_{CH}}\simeq\sqrt{\frac{12/13}{24/14}}=\sqrt{\frac7{13}}=0.734,
$$
so the pair would move approximately from $\pm375$ to \b[$\pm275$ mV]. A frozen-carbon estimate gives $1/\sqrt2$, or about 265 mV; the actual <normal mode> includes coupled motion. Whole-molecule modes change much less: the <molecular mass> rises only from approximately 41 to 44, giving a translational estimate $\sqrt{41/44}\simeq0.965$.
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