We report the first electric field dependence IR spectra of three cytosine tautomers solvated in helium nanodroplets. By using an electric field dependence on the three lowest energy tautomers of cytosine and ab initio calculations, we are able to measure the vibrational transition moment angles (VTMAs), specifically for the NH2 symmetric stretch (SS) mode in this study, with more precision; thus we have reassigned the previous NH2 (SS) VTMA of 74 o for the C1 tautomer to 85 o , which the

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... is in excellent agreement with the ab initio value. Nonplanarity of the three lowest energy tautomers of cytosine has been investigated by measuring the VTMA of each vibrational mode for the tautomers.