Articles you may be interested inElectronic spectra of the jet-cooled DNA base adenine were obtained by the resonant two-photon ionization ͑R2PI͒ and the laser induced fluorescence ͑LIF͒ techniques. The 0-0 band to the lowest electronically excited state was found to be located at 35 503 cm Ϫ1 . Well-resolved vibronic structures were observed up to 1100 cm Ϫ1 above the 0-0 level, followed by a slow rise of broad structureless absorption. The lowest electronic state was proposed to be of n * character, which lies ϳ600 cm Ϫ1 below the onset of the * state. The broad absorption was attributed to the extensive vibronic mixing between the n * state and the high-lying * state.

A multiphoton ionization study was carried out on hydrated clusters of DNA base adenine in supersonic molecular beams. Resonant two-photon ionization at 266 nm showed that the relative ion intensity between the hydrated clusters A m (H2O) n and the unhydrated ones was anomalously small, particularly for m = 1, in contrast to the case of electron impact ionization. The ratio was of the order of 10-2 for m = 1, 10-1 for m = 2, but about 1 for m ≥ 3. One-photon excitation to the first electronically excited state was found to be responsible for the extensive fragmentation of adenine monomer hydrates A1(H2O) n . The water acts as a proton-donating solvent whose hydrogen bonding with the solute becomes weakened in the n π* excited state, thereby giving the excited state its repulsive nature. Hydrates of adenine complex A m (H2O) n (m ≥ 2) tend to better survive the rupture of the water cage at higher m, probably because the energy transfer between adenine molecules is not sufficiently fast. The fragmentation was found to be less extensive at higher levels of excitation with a much weaker n π* character. Change of solvent to those of less proton-donating or even proton-accepting character systematically reduced the tendency of fragmentation.

Ultraviolet photodepletion spectra of dibenzo-18-crown-6-ether complexes with alkali metal cations (M+-DB18C6, M = Cs, Rb, K, Na, and Li) were obtained in the gas phase using electrospray ionization quadrupole ion-trap reflectron time-of-flight mass spectrometry. The spectra exhibited a few distinct absorption bands in the wavenumber region of 35 450−37 800 cm−1. The lowest-energy band was tentatively assigned to be the origin of the S0-S1 transition, and the second band to a vibronic transition arising from the “benzene breathing” mode in conjunction with symmetric or asymmetric stretching vibration of the bonds between the metal cation and the oxygen atoms in DB18C6. The red shifts of the origin bands were observed in the spectra as the size of the metal cation in M+-DB18C6 increased from Li+ to Cs+. We suggested that these red shifts arose mainly from the decrease in the binding energies of larger-sized metal cations to DB18C6 at the electronic ground state. These size effects of the metal cations on the geometric and electronic structures, and the binding properties of the complexes at the S0 and S1 states were further elucidated by theoretical calculations using density functional and time-dependent density functional theories.

In this Communication, the plus and minus signs of the circular dichroism (CD) spectra in Figures 2b and 4b were incorrect. The corrected Figures are shown below. Additionally,after further theoretical investigation, it was found that the signs of the rotatory strengths (R)for pseudoephedrine (pED) vary depending on the type of the density functionals used in the time-dependent density functional theory (TDDFT) calculations. This variation is due to small CD effects of the S 0-S 1 transition of pED and large error bars of the CD values predicted by theory.T able S1 in the Supporting Information lists the R values estimated using various density functionals. Figure 2. a) R2PI spectrum of S-pED near the origin band of the S 0-S 1 transition. The inset shows the structure of S-pED. The number of ions produced by as ingle-laser pulse at the origin bands was roughly estimated as about 900. b) R2PI CD spectra of S-(blue line) and R-pED (red line). The g values at the bands of AG(a), AG(b), and GG(a) of S-pED were measured as + + 0.026 AE 0.005, À0.025 AE 0.006, and + + 0.024 AE 0.005, respectively.c)Theoretical CD spectra of S-(blue line) and R-pED (red line) obtained with the rotatory strength, R,c alculated using TDDFT at the M06-2X/6-311 + ++ + G(d,p) level. Figure 4. a) R2PI spectrum of RED near the origin band of the S 0-S 1 transition. The inset shows the structure of RED. The discontinuous region between 37825 and 37855 cm À1 is where the grating order of the dye laser changes. b) R2PI CD spectrum of RED. The g values of 1-3 bands were measured as + + 0.030 AE 0.011, À0.091 AE 0.007,a nd + + 0.041 AE 0.013, respectively.