Infrared photodissociation spectra of [Mg•(H 2 O) 1-4 ] + and [Mg•(H 2 O) 1-4 •Ar] + are measured in the 3000-3800 cm -1 region. For [Mg•(H 2 O) 1-4 ] + , cluster geometries are optimized and vibrational frequencies are evaluated by density functional theory calculation. We determine cluster structures of [Mg•(H 2 O) 1-4 ] + by comparison of the infrared photodissociation spectra with infrared spectra calculated for optimized structures of [Mg•(H 2 O) 1-4 ] + . In the [Mg•(H 2 O) 1-3 ] + ions, all the water molecules are
Geometrical structures of iron oxide cluster cations have been analyzed by ion mobility mass spectrometry. The series of (FeO)n(+) and FenOn + 1(+) cluster cations were predominantly observed in a mass spectrum at high ion-injection energy into a drift cell. Arrival time distributions in the ion mobility spectrometry indicate that two structural isomers coexist for the (FeO)n(+) clusters at n ≥ 5. By comparison of experimental collision cross sections determined from the arrival times with theoretical ones, two-dimensional ring and sheet structures were assignable for (FeO)n(+) (n = 3-8). In addition to these isomers, compact three-dimensional structures were also found to be stable at (FeO)n(+) (n ≥ 6). Thus, the two-dimensional and three-dimensional structural isomers coexist for (FeO)n(+) (n = 6-8).
We have studied 3s(n-1 and pi-1) Rydberg states and D0(n-1) and D1(pi-1) cationic states of pyrazine [1,4-diazabenzene] by picosecond (2 + 1) resonance-enhanced multiphoton ionization (REMPI), (2 + 1) REMPI photoelectron imaging, He(I) ultraviolet photoelectron spectroscopy (UPS), and vacuum ultraviolet pulsed field ionization photoelectron spectroscopy (VUV-PFI-PE). The new He(I) photoelectron spectrum of pyrazine in a supersonic jet revealed a considerably finer vibrational structure than a previous photoelectron spectrum of pyrazine vapor. We performed Franck-Condon analysis on the observed photoelectron and REMPI spectra in combination with ab initio density functional theory and molecular orbital calculations to determine the equilibrium geometries in the D0 and 3s(n-1) states. The equilibrium geometries were found to differ slightly between the D0 and 3s states, indicating the influence of a Rydberg electron on the molecular structure. The locations of the D1-D0 and 3s(pi-1)-3s(n-1) conical intersections were estimated. From the line width in the D1 <-- S0 spectrum, we estimated the lifetime of D1 to be 12 fs for pyrazine and 15 fs for fully deuterated pyrazine. A similar lifetime was estimated for the 3s(pi-1) state of pyrazine by REMPI spectroscopy. The vibrational feature of D1 observed in the VUV-PFI-PE measurement differed dramatically from that in the UPS spectrum, which suggests that the high-n Rydberg (ZEKE) states converging to the D1 vibronic state are short-lived due to electronic autoionization to the D0 continuum.
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