Ko-ichi Sugawara

Observation of the infrared spectra of the NH2-stretching vibration modes of anilineArn (n = 1, 2) clusters in a supersonic jet using REMPI

Abstract The infrared spectra of the NH2 stretching modes of anilinen (n = 1, 2) clusters and corresponding cluster cations in a supersonic jet have been observed using an IR-REMPI double resonance technique. The observed frequencies of the anilineAr cluster are νsym = 3422, and νasym = 3508 cm−, and those of the aniline-Ar+ cation are νsym = 3395 and νasym = 3489 cm−. The frequency shifts of the NH2 stretching modes due to the Ar atoms have been found to be small. The aniline-Ar+ cluster ionized by the REMPI method has been found to be cold and the infrared spectrum shows not hot bands from the van der Waals modes, even though the excess energy above the ionization is as much as 5600 cm−1. A process which gives the cold clusters is discussed.

Energy profile of the interconversion path between T-shape and slipped-parallel benzene dimers

The energy profile of the interconversion path between the T-shape and slipped-parallel dimers has been studied by high level ab initio calculations. The CCSD(T) (coupled cluster calculation with single and double substitutions with noniterative triple excitations) interaction energy at the basis set limit has been estimated from the MP2 (the second-order Moller–Plesset calculation) interaction energy near the basis set limit and the CCSD(T) correction term using the 6-311G* basis set. The calculated CCSD(T) level energy profile has shown that the potential is very flat and the interconversion barrier height is very small (around 0.2 kcal/mol). The MP2 calculations using large basis sets near the basis set limit considerably overestimate the attraction of the slipped-parallel dimer, which indicates the importance of higher level electron correlation correction for studying the potential energy surface of the benzene dimer.

Reactions of gold cluster cations Aun+ (n=1-12) with H2S and H2

The reactions of gold cluster cations Aun+ (n=1–12) with H2S and H2 have been studied using Fourier-transform ion-cyclotron resonance (FT–ICR) mass spectrometry. The cluster cations were produced by laser ablation of a gold rod in He atmosphere, and their reactions were observed at room temperature and low total pressures of 10−7–10−5 Torr. Initial products of the reactions with H2S were mainly AuSH+ for n=2, AunS+ for n=4–8 and 10, and AunSH2+ for n=9, 11, and 12. No reactions of Au+ and Au3+ with H2S were observed. Even n cluster cations were more reactive than adjacent odd n clusters. The particularly low reactivity at n=1, 3, 9, and 11 is consistent with the low ionization potential of Aun and the weak binding energy of Aun+–Au. Further sulfuration reactions of AunS+ proceeded to give AunSm+ and finally stopped at AunSm+xH2+ when H2 release did not occur. The maximum number of sulfur atoms m+x increased with the cluster size up to n=8, while the sulfuration reaction stopped at early stages for n⩾9. In...

Energy-resolved collision-induced dissociation of Cun+ (n=2–9): Stability and fragmentation pathways

Collision induced dissociation of Cun+ clusters (n=2–9) in collision with Xe is presented in the center-of-mass energy range from about 100 meV to above 15 eV. The collision energy dependence is measured for the total and the partial dissociation cross sections, and the dissociation thresholds for the dominating processes are derived. The threshold energies show pronounced odd–even alternations, reflecting a higher stability of the odd-numbered, Cu2n+1+, clusters. Further, the evaporation of a single neutral atom is found to be the energetically favorable process for the even-numbered clusters, while the loss of the neutral dimer is favorable in the case of the odd-numbered clusters. An exception is Cu9+, where the formation of Cun−1+ is energetically favorable, and the energetics of the Cun−2+ formation are in good agreement with sequential evaporation of two neutral monomers. Here we discuss the energy dependency of the total and partial dissociation cross sections, and try to give a consistent picture ...

Infrared depletion spectroscopy of aniline-NH3 and aniline-NH3+ clusters in a supersonic jet

Abstract The vibrational spectra of aniline-NH 3 and aniline-NH 3 + clusters in the NH stretching vibration region have been measured using infrared depletion spectroscopic techniques combined with mass spectrometry. There are two strong absorption bands at 3354 and 3479 cm −1 in the spectrum of aniline-NH 3 . They have been assigned to the stretching vibrations of the NH 2 group of aniline. One of the NH bonds of aniline interacts with the lone pair of the nitrogen atom of NH 3 through the hydrogen bond. The spectrum of aniline-NH 3 + gives only one strong absorption at 3419 cm −1 . This band has been assigned to the stretching vibration of the free NH bond of aniline. The hydrogen bond in the cation cluster has been found to be much stronger than that in the neutral cluster.

INFRARED SPECTROSCOPY OF ANILINE-X (X = N2, CH4, CHF3, CO) CLUSTERS AND THEIR CORRESPONDING CLUSTER CATIONS IN THE NH2-STRETCHING VIBRATION REGION

Abstract The NH 2 -stretching vibrational modes of four different aniline-X clusters (X = N 2 , CH 4 , CHF 3 , CO) and their corresponding cluster cations were investigated by ion-depletion spectroscopy. The observed frequency shifts of the neutral clusters have been found to be very small, and to be proportional to the red shift of the origin of the S 1 ← S 0 electronic band. This result suggests that the molecules interact with the aromatic ring system of aniline. The shifts of the cation species are larger than those of the neutral species, especially for aniline-CH 4 + . The proton affinity of the interacting molecule has been found to be correlated to the frequency shift except for CHF 3 . The different behavior of the cation species from the neutral ones suggests that the main interaction force in the cation clusters is different from that in the neutral ones. The possibility of the hydrogen bond interaction is discussed.

Rate constant measurements for reactions of SiH3 with O2, NO and NO2 using time-resolved infrared diode laser spectroscopy

Abstract The rate constants for the reactions SiH3+O2, SiH3+NO2 and SiH3+NO+N2 have been measured over the pressure range 1–10 Torr at 300 K, by monitoring a SiH3 absorption line at 719.931 cm−1 using time-resolved diode laser spectroscopy. SiH3 radicals were prepared by pulsed CO2 laser photolysis of CCl3F in SiH4: CCl3F + nhv → CCl2F + Cl, Cl + SiH4 → HCl + SiH3. Analysis of the pseudo-first-order decay of SiH3 provided rate constants of (1.3 ± 0.3) × 10−11 and (5.1 ± 0.9) × 10−11 cm3 molecule−1 s−1 (±2σ) for the reactions with O2 and NO2 respectively and 8.2 ± 0.9 × 10−30 cm6 molecule−2 s−1 (±2σ) for the reaction SiH3 + NO + N2.

Vibrational and rotational energy distributions of CH3 and IF formed in the reactions of F atoms with CH4 and CH3I

The two reactions F+CH4→CH3+HF (1) and F+CH3I→CH3+IF (2) have been investigated by using time‐resolved diode laser absorption spectroscopy to probe the reaction products CH3 and IF. The fluorine atoms have been generated by the pulsed CO2 laser photolysis of SF6 in the presence of CH4 or CH3I at a total pressure of 5 Pa. Rotational lines of CH3 in the v2 =1–0, 2–1, and 3–2 bands (out‐of‐plane bending vibration) and those of IF in the v=1–0, 2–1, 3–2, 4–3, 5–4, and 6–5 bands have been observed and analyzed to determine time‐dependent product energy distributions. No clear evidence for population inversion has been found in the vibrational levels of both CH3 and IF. Nascent vibrational distributions of v2=0: 1: 2 of CH3 are 1:0.36:0.15 for reaction (1) and 1:0.32:0.14 for reaction (2), and that of IF v=0:1:2:3:4:5 is 1:0.70:0.40:0.22:0.10:0.04. The nascent CH3 produced in reaction (1) is rotationally cold (around room temperature) and only 3% and 2% of total available energy are partitioned to the ν2 vibrat...

Electronic spectrum of AgNH3 complex

Abstract The electronic spectrum of the silver–ammonia 1:1 complex AgNH 3 has been observed for the first time. The complex was formed using laser ablation and cooled in a free jet expansion, and its spectrum was observed through resonantly enhanced multiphoton ionization (REMPI). The origin of the A–X band system of AgNH 3 located at 467 nm is red-shifted from the corresponding Ag 5p 2 P 1/2 –5s 2 S transition by 8142 cm −1 , indicating a significant stabilization upon electronic excitation. The vibrational frequency of the intermolecular stretching mode in the A state was determined to be 378 cm −1 .

Observation of infrared absorption spectra of molecular ions, H3+ and HN2+, by FTIR spectroscopy

Abstract The infrared absorption spectra of the molecular ions H 3 + and HN 2 + were measured by using the Fourier-transform infrared method and a hollow-cathode discharge cell. From the analysis of the relative intensities and the linewidths of the absorption lines, these ions in the ground vibrational states were found to be well thermalized in the cell. The band center of the v 1 mode of HN 2 + has been determined to be 3233.9608(2) cm −1 which is slightly higher than the literature value.