Kenro Hashimoto

Structures, stabilities and ionization potentials of Na(H2O) n and Na(NH3)n (n= 1–6) clusters. An ab initio MO study

Abstract The structure and stability of Na(H2O)n and Na(NH3)n (n=1–6) have been calculated at the HF/3–21G level. For n⩾4 Na(H2O)n is a surface complex, where Na atom tends to be situated on the surface of (H2O)n cluster. Na(NH3)n is an inclusion complex where Na is surrounded by NH3 molecules. Water—water hydrogen bonds play an essential role in stabilizing Na(H2O)n, whereas stabilization by NaN bond formation is more important for Na(NH)n. Calculated ionization potentials as functions of n can reproduce qualitatively the experimentally found different trends between Na(H2On and Na(NH3)n, which are related to the above-mentioned different structural features.

Hydrogen transfer in photo-excited phenol'ammonia clusters by UV-IR-UV ion dip spectroscopy and ab initio molecular orbital calculations. II. Vibrational transitions

The electronic spectra of reaction products via photoexcited phenol/ammonia clusters (1:2–5) have been measured by UV-near-IR–UV ion dip spectroscopy. Compared with the electronic spectra of hydrogenated ammonia cluster radicals the reaction products have been proven to be (NH3)n−1NH4 (n=2–5), which are generated by excited-state hydrogen transfer in PhOH–(NH3)n. By comparing the experimental results with ab initio molecular orbital calculations at multireference single and double excitation configuration interaction level, it has been found that the reaction products (NH3)n−1NH4 (for n=3 and 4), contain some isomers.

Photochemistry of phenol–(NH3)n clusters: Solvent effect on a radical cleavage of an OH bond in an electronically excited state and intracluster reactions in the product NH4(NH3)n−1 (n⩽5)

The potential energy surfaces of PhOH–(NH3)0,1 and NH4(NH3)1–4 have been investigated theoretically by ab initio methods. Intermolecular stretching in PhOH–NH3 assists in the radical cleavage of an OH bond occurring through a ππ*/πσ* potential crossing. Thus, excited state hydrogen transfer (ESHT) is expected to take place by a solvent-assisted mechanism even in the larger PhOH–(NH3)n. Because sufficient energy is obtained by ESHT from PhOH–(NH3)n (ππ*) to PhO–NH4(NH3)n−1 (πσ*) (n⩽5), hydrogen relocation and/or ammonia migration in the product NH4(NH3)n−1 can readily follow ESHT, which is responsible for observing isomer bands in the absorption spectra of the photoinduced reaction products of PhOH–(NH3)n.

Electronically Excited States of Sodium-Water-Clusters

The lowest electronically excited state of small Na(H2O)n clusters has been investigated experimentally and theoretically. The excitation energy as determined by the depletion spectroscopy method drops from 16 950 cm−1 for the sodium atom down to 9670 cm−1 when only three water molecules are attached to the Na atom. For larger clusters the absorption band shifts back towards higher energies and reaches 10 880 cm−1 for n=12. The experimental data are compared to quantum-chemical calculations at the Moeller–Plesset second-order perturbation and multireference single and double excitation configuration interaction levels. We found that the observed size dependence of the transition energy is well reproduced by the interior structure where the sodium atom is surrounded by water molecules. The analysis of the radial charge distribution of the unpaired electron in these interior structures gives a new insight into the formation of the “solvated” electron.

Ab initio theoretical study of ‘surface’ and ‘interior’ structures of the Na (H2O)4 cluster and its cation

Abstract The structures and stabilities of Na(H2O)4 and its cation have been investigated at the ab initio HF/6-31+G(d), HF/6-31++G(d, p) and MP2/6-31+G(d) levels. For the neutral complex, both the ‘surface’ structure and the ‘interior’ structure are found to be minima on the potential energy surface. The energies of these two structures are close to each other at the highest level. For both surface and interior structures, some characteristic features are found in the vibrational spectra, which may be the best method for experimental identification. For the cation cluster, only the ‘interior’ structure is stable.

Picosecond time-resolved infrared spectra of photo-excited phenol–(NH3)3 cluster

Abstract Picosecond time-resolved IR spectra of phenol–(NH3)3 have been measured by UV–IR–UV ion dip spectroscopy for the first time. It was found that the time-evolution of two vibrational bands at 3180 and 3250 cm −1 is different from each other. The results show that two transient species are generated from the photo-excited phenol–(NH3)3 cluster. From ab initio calculation, the transient species are assigned to two isomers of (NH3)2NH4.

Study on microscopic solvation process of Li atom in ammonia clusters: photoionization and photoelectron spectroscopies of M(NH3)n (M = Li, Li−)

Photoionization and photodetachment processes of M(NH3)n = (M = Li and Li−) are investigated. Ionization potentials (IPs) of Li(NH3)n (5 ⩽ n ⩽ 28) are found to decrease monotonously with increasing n and give IP(∞ as 1.47 eV, in agreement with the photoelectric threshold of liquid NH3. Photoelectron spectra of Li−(NH3)n (n ⩽ 10) exhibit a rapid decrease in the Li(2P)−Li(2S) separation and a red-shift of the Li(2S)−Li−(1S) type transition with increasing n. Based on these results as well as the theoretical results on the geometrical and electronic structures, we discuss the solvation state of the Li atom in (NH3)n relating to the solvated-electron formation.

Hydrogen transfer dynamics in a photoexcited phenol/ammonia (1:3) cluster studied by picosecond time-resolved UV-IR-UV ion dip spectroscopy

The picosecond time-resolved IR spectra of phenol/ammonia (1:3) cluster were measured by UV-IR-UV ion dip spectroscopy. The time-resolved IR spectra of the reaction products of the excited state hydrogen transfer were observed. From the different time evolution of two vibrational bands at 3180 and 3250 cm(-1), it was found that two isomers of hydrogenated ammonia radical cluster .NH(4)(NH(3))(2) coexist in the reaction products. The time evolution was also measured in the near-IR region, which corresponds to 3p-3s Rydberg transition of .NH(4)(NH(3))(2); a clear wavelength dependence was found. From the observed results, we concluded that (1) there is a memory effect of the parent cluster, which initially forms a metastable product, .NH(4)-NH(3)-NH(3), and (2) the metastable product isomerizes successively to the most stable product, NH(3)-.NH(4)-NH(3). The time constant for OH cleaving, the isomerization, and its back reaction were determined by rate-equation analysis to be 24, 6, and 9 ps, respectively.

Ab initio MO study of solvated negative alkali atom clusters: [M(H2O)n]− and [M(NH3)n]− (M Na and Li, n = 1−3)

Abstract The structures, stabilities and vertical electron detachment energies (VDEs) of [Na(H 2 O) n ] − , [Na(NH 3 ) n ] − and [Li(NH 3 ) n ] − ( n = 1−3) are investigated by the ab initio MO method at the correlated level. The NaH interactions and hydrogen bonds are important in [Na(H 2 O) n ] − , while the metal-N bonds become essential in stabilizing the [Na(NH 3 ) n ] − and [Li(NH 3 ) n ] − with increasing n . The size dependence of the VDEs of [Na(H 2 O) n ] − differs from that of [Na(NH 3 ) n ] − and [Li(NH 3 ) n ] − due to their structural features. In addition, the geometries and VDEs of [Li(H 2 O) n ] − ( n = 1−3) are predicted theoretically. The size dependence of their VDEs is similar to that of [Na(NH 3 ) n ] − and [Li(NH 3 ) n ] − rather than [Na(H 2 O) n ] − .

RESONANCE-ENHANCED MULTIPHOTON ELECTRON DETACHMENT SPECTRUM OF C5-

The resonance‐enhanced multiphoton electron detachment spectrum of C5− was measured. The peaks observed at 470–500 nm were assigned to be 1 photon excitation of 2Πu to the 2Πg state. The vibrational structure gives the symmetric stretching frequency of ν2=718±43 cm−1 for the excited state of C5−.