Toshinori Suzuki

Stimulated-emission ion-dip spectra of phenol–H 2 O hydrogen-bonded complex: estimation of intramolecular vibrational redistribution rates of ground-state vibrational levels

Stimulated-emission ion-dip spectroscopy was applied for the observation of the ground-state vibrational levels of jet-cooled phenol and its hydrogen-bonded complex with water. The observed ion-dip intensity, representing the stimulated emission from S1 to the vibrational level in S0 yields information about the intramolecular vibrational redistribution rate of the vibrational state. The intramolecular vibrational redistribution rate was estimated from the observed ion-dip intensities for the above species. It was found that a great enhancement of the intramolecular vibrational redistribution rate occurs with the formation of the hydrogen-bonded complex. The enhancement is ascribed to the increase of the density of the vibrational states contributed by the low-frequency hydrogen-bond modes.

Intersystem crossing in jet-cooled naphthalene, α- and β-chloronaphthalene as studied by sensitized phosphorescence excitation spectroscopy

Abstract The fluorescence excitation and sensitized phosphorescence excitation spectra of jet-cooled naphthalene- h 8 , - d 8 , α-chloro naphthalene, β-chloronaphthalene have been measured. It is shown that the intersystem crossing efficiency of naphthalene is large for specific vibronic levels in S 1 . This efficiency is due to an accidental resonance with the vibronic level belonging to nearby T 2 state. Cl atom accelerates the intersystem crossing rate of naphthalene by about two orders of magnitude.

Dispersed fluorescence spectra of jet‐cooled benzene from the levels near the channel three threshold

Highly resolved dispersed fluorescence spectra from single vibronic levels lying 2594–3084 cm−1 above the 1B2u origin of benzene have been measured in a supersonic jet. The dispersed fluorescence spectra from the levels 6110211, 6117211, 71 lying below the threshold of the third channel consist of very sharp lines, while the spectrum from the 6113 level lying above the threshold contains a large amount of broad emission due to a fast intramolecular vibrational redistribution (IVR) process.

Ion dips in two-color photoionization spectra of jet-cooled trans-stilbene stimulated transitions to ground-state vibrational levels

Abstract The two-color photoionization spectra of jet-cooled trans-stilbene heve been measured. The ion dips appearing in the region above the adiabatic ionization potential were found to be due to the stimulated emission from the intermediate state to the ground-state vibrational levels. The observation of highly excited Rydberg states is also reported.

Synthesis of η2-cyclooctene iridium and rhodium complexes supported by a novel P,N-chelate ligand and their reactivity toward hydrosilanes: facile Cl migration from metal to silicon via silylene complex intermediates and formation of a base-stabilised silylene complex

η2-Cyclooctene iridium and rhodium complexes bearing a P,N-chelate ligand C6H3Me-3-PCy2-4-NMe2 (abbreviated as PcyN), (PcyN-P,N)MCl(η2-coe) (1: M = Ir, 2: M = Rh), were synthesised and reactions toward several sterically hindered hydrosilanes were investigated to clarify their reactivity. The reaction of 1 with H2SiMes2 (Mes = mesityl = 2,4,6-trimethylphenyl) proceeded at 40 °C to give a di-iridium complex bridged by a chlorosilylene ligand (PcyN-P,N)2Ir2H2(μ-Cl)(μ-H)(μ-SiClMes) (5). The reaction of 1 with HSiMe2SiMes2Me occurred at room temperature to afford HSiMesMe2 and a silyl complex 6 formed by metallation of an ortho-methyl group of Mes, which slowly dimerised to give a dinuclear complex containing a chlorosilyl ligand (PcyN-P,N)2Ir2H(μ-Cl)(μ-H)[μ-SiMeCl(C6H3-2,4-Me2-6-CH)-Si,C,C] (7). The formation of complexes 5, 6 and 7 suggests that facile migration of Cl from Ir to Si occurs probably via silylene iridium intermediates. Treatment of 1 with HSiMe2SiMe2OMe at room temperature yielded a methoxy-bridged bis(silylene) complex (PcyN-P,N)IrHCl[SiMe2··O(Me)··SiMe2-Si,Si] (8) quantitatively, whose X-ray crystal structure was determined as the first iridium complex of this type. The reactions of 1 and 2 with a bulky trihydrosilane H3SiC(SiMe3)3 underwent an intramolecular γ-Si–Me activation to afford (PcyN-P,N)MHn[SiMe2C(SiMe3)2SiClMe-Si,Si] (9: M = Ir, n = 3; 10: M = Rh, n = 1). Complex 1 even reacted with an extremely sterically hindered terphenylhydrosilane H3SiDmp (Dmp = 2,6-dimesitylphenyl) in the presence of PMe3 to give a chlorosilyl complex (PcyN-P,N)IrH2(PMe3)(SiHClDmp) (11) without intramolecular bond activation. Complex 1 also reacted with H3SiTrip (Trip = 2,4,6-triisopropylphenyl) in the presence of excess 4-(dimethylamino)pyridine (DMAP) at room temperature to give a chlorido(dihydrosilyl) complex (PcyN-P,N)IrHCl(DMAP)(SiH2Trip) (12) instantaneously. Treatment of complex 12 with LiB(C6F5)4·2.5Et2O provided a cationic DMAP-stabilised silylene complex [(PcyN-P,N))IrH2(DMAP)(SiHTrip ← DMAP)][B(C6F5)4] (13).

SRVL fluorescence spectra of SO2 in a supersonic free jet. c-axis coriolis interaction

Abstract The single rovibronic level (SRVL) fluorescence spectra of the E band of SO 2 in a supersonic free jet have been measured. It was found that the forbidden transition observed in the fluorescence spectra is induced by a c -axis Coriolis interaction in the excited state.

Transient scattering of dipole field from a conducting cylinder buried in a lossy medium

The properties of transient electromagnetic fields transmitted from an antenna and scattered from buried objects are investigated in connection with the radar imaging of an invisible target (e.g., underground imaging). The early-time scattering fields are calculated exactly when a short horizontal dipole is located over the interface separating air and the lossy medium, and a perfectly conducting infinite cylinder is buried in the lossy medium. The approximate transient scattering fields are also derived and compared with the exact transient field. It is shown that the present approximation is good when the antenna deviates from directly over the buried cylinder, but invalid when the antenna is located over the buried cylinder. It is also found that the geometrical-optics approximation is effective only when the propagation path is nearly normal to the ground surface.<<ETX>>

Performance analysis and evaluation of co‐channel interference canceler for DS‐CDMA using replica suppression

Multistage interference cancelers are deemed to be one of the most realizable schemes for asynchronous DS-CDMA. While limited to SD (Soft Decision)-based parallel multistage cancellation, this paper covers (1) theoretical relations introduced between suppressing factors and interference canceling gains, and (2) computer simulation results confirming the validity of the theory. There are two ways of setting suppressing factors. One is to set common values for all stages, and another is to set an individual value for each stage. This paper also discusses the differences between the two types of setting suppressing factors.

IVR of Van der Waals and Hydrogen-Bonded Complexes as Studied by Stimulated Emission Ion Dip Spectroscopy

Intramolecular vibrational redistribution (IVR) is an important nonradiative process in an isolated large molecule, and it is being extensively studied experimentally and theoretically. Especially, IVR in electronically excited state has been studied by various experimental means such as fluorescence excitation, dispersed fluorescence spectro-scopies and the measurement, of fluorescence life-time.1 As a result, our information on IVR for electronically excited states is now considerably accumulated. On the other hand, the study on IVR in electronically ground-state is very few. This is due to lack of suitable experimental means. The study by infrared radiation is an orthodox way. However, because of poor time response of the infrared detection and of severe selection rule for infrared absorption, the IVR study of a ground state molecule by infrared light is greatly restricted. Instead of direct vibrational excitation by infrared light, the ground-state vibrational level of an isolated nolecule can be populated by stimulated emission from an electronically excited state, say, S1 state with UV/visible laser light (v2). One of the stimulated emission methods is “stimulated emission pumping” in which the stimulated emission from S1 to a ground-state vibrational level is monitored by the dip of the fluorescence from the S1 level pumped with vl2–3 The depth of the fluorescence dip represents the decrease of the S1 state population which is determined by the balance of loss of the S1 state population by the stimulated emission with v2 and the gain of the population by the reabsorption with same v2 from the ground-state vibrational level. When the life-time of the ground-state vibrational level to which the stimulated emission occurs is long, the molecules in the vibrational level have a great chance to come back to S1, resulting in a small fluorescence dip. Conversely, when the life-time (decay rate) is short (large), we have a large dip. Since the lifetime of the ground-state vibrational level of an isolated molecule is in most cases determined by IVR process, we can obtain the IVR rate from the observed depth of the fluorescence dip. Therefore, the depth of the fluorescence dip measured in percentage relative to the fluorescence signal in absence of the stimulated emission provides us with very useful information on the IVR rate of ground-state vibrational level. However, the quantitative determination of the percentage fluorescence dip depth is very difficult because it requires complete spatial matching of the two laser beams v1 and v2. The observed percentage dip depth sensitively varies by mismatching of the two beams whose elimination is practically impossible.