Tomonari Wakabayashi

Infrared spectroscopic study of rovibrational states of methane trapped in parahydrogen crystal

The ν3 and ν4 vibrational transitions of methane trapped in solid parahydrogen have been observed by using Fourier transform infrared and high resolution laser spectroscopy. The observed spectrum is interpreted in terms of rovibrational states of the spherical rotor which are subjected to the crystal field splitting. The ν4 band shows extremely sharp lines of a width of ∼0.003 cm−1, while the ν3 band exhibits broader lines of a width of 1 cm−1. The infrared selection rules derived from an extended group theory to take into account the field effect are consistent with the observed spectra. The intermolecular interaction and the field effect in solid parahydrogen are analyzed quantitatively.The ν3 and ν4 vibrational transitions of methane trapped in solid parahydrogen have been observed by using Fourier transform infrared and high resolution laser spectroscopy. The observed spectrum is interpreted in terms of rovibrational states of the spherical rotor which are subjected to the crystal field splitting. The ν4 band shows extremely sharp lines of a width of ∼0.003 cm−1, while the ν3 band exhibits broader lines of a width of 1 cm−1. The infrared selection rules derived from an extended group theory to take into account the field effect are consistent with the observed spectra. The intermolecular interaction and the field effect in solid parahydrogen are analyzed quantitatively.

High Resolution Infrared Absorption Spectra of Methane Molecules Isolated in Solid Parahydrogen Matrices

We present high resolution (∼0.01 cm−1) infrared absorption spectra of the ν4 band of methane doped parahydrogen (CH4/pH2) solids produced by two different techniques: gas condensation in an enclosed cell at T≈8 K, and rapid vapor deposition onto a T≈2 K substrate in vacuum. The spectrum of the rapid vapor deposited solid contains a novel progression of single peaks with ≈5 cm−1 spacing, superimposed over the known spectrum of CH4 molecules trapped in sites of D3h symmetry in hexagonal close-packed (hcp) solid pH2. New theoretical calculations of the rovibrational transitions of a tetrahedral molecule in an external field of Oh symmetry permit the assignment of this new progression to CH4 molecules trapped in crystalline face centered cubic (fcc) regions of the pH2 solid. Annealing of the rapid vapor deposited samples to T≈5 K decreases the intensities of the CH4/pH2(fcc) absorptions, and results in intensity changes for parallel and perpendicularly polarized CH4/pH2(hcp) transitions. We discuss these phe...

Binding motif of terminal alkynes on gold clusters.

Gold clusters protected by terminal alkynes (1-octyne (OC-H), phenylacetylene (PA-H) and 9-ethynyl-phenanthrene (EPT-H)) were prepared by the ligand exchange of small (diameter <2 nm) Au clusters stabilized by polyvinylpyrrolidone. The bonding motif of these alkynes on Au clusters was investigated using various spectroscopic methods. FTIR and Raman spectroscopy revealed that terminal hydrogen is lost during the ligand exchange and that the C≡C bond of the alkynyl group is weakened upon attachment to the Au clusters. Acidification of the water phase after the ligand exchange indicated that the ligation of alkynyl groups to the Au clusters proceeds via deprotonation of the alkynes. A series of precisely defined Au clusters, Au34(PA)16, Au54(PA)26, Au30(EPT)13, Au35(EPT)18, and Au(41-43)(EPT)(21-23), were synthesized and characterized in detail to obtain further insight into the interfacial structures. Careful mass analysis confirmed the ligation of the alkynes in the dehydrogenated form. An upright configuration of the alkynes on Au clusters was suggested from the Au to alkyne ratios and photoluminescence from the excimer of the EPT ligands. EXAFS analysis implied that the alkynyl carbon is bound to bridged or hollow sites on the cluster surface.

Selective synthesis of organogold magic clusters Au54(C≡CPh)26.

Organogold clusters Au(54)(C(2)Ph)(26) were selectively synthesized by reacting polymer-stabilized Au clusters (1.2 ± 0.2 nm) with excess phenylacetylene in chloroform.

Polyyne cyclization to form carbon cages: [16.16.16](1,3,5)cyclophanetetracosayne derivatives C60H6 and C60Cl6 as precursors to C60 fullerene

Abstract [16.16.16](1,3,5)Cyclophanes fused by six [4.3.2]propellatriene units, which would serve as precursors to cage polyyne C 60 H 6 and its perchloro derivative C 60 Cl 6 , respectively, were prepared. In the negative mode laser desorption mass spectra of the cyclophanes, the polyyne anions C 60 H 6 − and C 60 Cl 6 − were detected. Moreover, size-selective formation of C 60 + as well as C 60 − was also observed, indicating the possible polyyne cyclization mechanism to form the fullerene cage.

Tunneling chemical reactions in solid parahydrogen: A case of CD3+H2→CD3H+H at 5 K

Ultraviolet photolysis of CD3I in solid parahydrogen at 5 K gives CD3 radical, which decreases in a single exponential manner with a rate constant of (4.7±0.5)×10−6 s−1. Concomitantly, CD3H is formed, which is accounted for by the quantum tunneling reaction CD3+H2→CD3H+H. Under the same conditions, CH3I yields CH3 radical, but the corresponding reaction between CH3 and H2, expected to give CH4+H, does not proceed measurably at 5 K. The difference between the two systems is attributed to the difference in the zero point energy change.

High-resolution laser spectroscopy of methane clusters trapped in solid parahydrogen

Clusters of methane are isolated in solid parahydrogen. The vibrational spectral region of the ν4 fundamental of methane molecule is surveyed with a Fourier transform infrared spectrometer and a high-resolution difference-frequency infrared laser system. More than 200 sharp absorption lines are discovered whose linewidth is as narrow as 0.007 cm−1 (200 MHz). The spectrum indicates that the rovibrational levels of the clusters of small sizes are well quantized in solid parahydrogen.

Infrared spectroscopic study of rovibrational states of perdeuterated methane (CD4) trapped in parahydrogen crystal

The triply degenerate stretching (ν3) and bending (ν4) modes of CD4 in solid parahydrogen at cryogenic temperatures are studied by Fourier transform infrared spectroscopy to reveal crystal field split rovibrational structures. The observed spectra are analyzed by taking into account the crystal field potential which is constructed by the summation of the pairwise (dispersive) potential between the methane and the surrounding hydrogen molecules. By the least-squares fitting of that observed to a theoretical model the molecular constants of CD4 as well as the potential coefficient are determined as in the previous work on the CH4/p-H2 system. The potential is approximated to be proportional to the product of the polarizability of hydrogen molecule, the dipole–quadrupole polarizability of methane, and the inverse of the seventh power of the intermolecular distance between methane and hydrogen molecules. From the ratio of the potential coefficients of CH4 and CD4 the dipole–quadrupole polarizability of CD4 is...

Photoinduced reactions of methyl radical in solid parahydrogen

Photolysis of methyl iodide in solid parahydrogen (p-H2) at about 5 K is studied with ultraviolet light at 253.7 and 184.9 nm. It is found that the light at 253.7 nm produces only methyl radical, whereas the light at 184.9 nm yields both methyl radical and methane. The mechanism of the formation of the photoproducts is elucidated by analyzing the temporal behavior of the observed vibrational absorption. It is concluded that methyl radical in the ground state does not react with p-H2 molecules appreciably but that the radical in the electronic excited state of B(2A1′), accessible by reabsorption of 184.9 nm photons by the radical, decomposes to a singlet methylene CH2 a(1A1) and a hydrogen atom (2S) and that the singlet methylene reacts with a p-H2 molecule to give methane.

Mass spectroscopic studies of laser ablated carbon clusters as studied by photoionization with 10.5 eV photons under high vacuum

Neutral carbon clusters Cn (n=1–30) produced along with ionic clusters in laser vaporized graphite are studied under high vacuum by combined use of time-of-flight (TOF) mass spectroscopy and one photon ionization with a photon energy of 10.5 eV. The TOF mass distribution pattern shows intensification of the C4n+2 (n⩾2) clusters more clearly than the previous work by Kaizu et al. [J. Chem. Phys. 106, 9954 (1997)] who employed the same 10.5 eV photon but photoionized the neutral clusters generated by laser vaporization of graphite in helium buffer gas. The intensification is attributed to the intrinsic stability of the C4n+2 (n⩾2) neutral clusters, probably due to the monocyclicity. Two different line shapes of the mass spectral peak are observed for one and the same cluster size. The line shape with a tailing toward longer flight times is associated with the neutral clusters produced by relatively slow fragmentation of larger clusters (n≫30) followed by autoionization of the fragmented clusters. The other ...