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By supersonic jet: The rotational spectrum of guanine was investigated by laser ablation molecular beam Fourier transform microwave (LA MB FTMW) spectroscopy. The N7H keto, N9H keto, N9H enol trans, and N9H enol cis forms (see structures) were identified conclusively in the supersonic expansion from the experimental values of the rotational constants.
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Alonso et al. (2009) studied this question.
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