High resolution microwave spectra of the a-type, J = 1-0, transitions of He(N = 1-6)-H(12)C(14)N, He(N = 1-6)-H(13)C(14)N, He(N = 1-6)-H(12)C(15)N, He(N = 1-7)-D(12)C(14)N, and He(N = 1-6)-D(13)C(14)N clusters produced in a supersonic jet expansion were measured and analyzed. The resulting effective rotational constants, B(eff), initially decrease with the number of the attached helium atoms before reaching a minimum at N = 3 helium atoms for all isotopologues. The subsequent increase in B(eff) for N ≥ 4 is indicative of the onset of microscopic superfluidity. Comparison of our experimental B(eff) constants with those from quantum Monte Carlo simulations [A. A. Mikosz, J. A. Ramilowski, and D. Farrelly, J. Chem. Phys. 125, 014312 (2006)] reveals a nearly congruent trend in B(eff) for N up to 6. Analysis of the hyperfine structure of the (14)N containing isotopologues yielded a gradual incremental increase in the magnitude of χ(aa) and for N = 1-6, which suggests the internal rotation of the HCN molecule is becoming increasingly hindered.

The effect of the N1 ribose sugar on the initial excited‐state structural dynamics of uridine is explored with ultraviolet resonance Raman spectroscopy. Excited‐state slopes and broadening parameters were obtained by simulating the resonance Raman excitation profiles and absorption spectrum using a self‐consistent, time‐dependent formalism. The initial excited‐state structural dynamics of uridine look similar to those of uracil, in terms of the distribution of percentage of reorganization energy along different modes, but there is an overall decrease in the excited‐state slopes along most of the modes in uridine compared with uracil. Only about 30% of the total initial reorganization energy in both uracil and uridine are oriented along the photochemically reactive coordinates. The results are also similar to those of thymine and thymidine, upon attachment of the sugar. These differences between thymine, thymidine, uracil and uridine are examined, and the possible effect on the resulting differences in photochemistry is discussed.

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