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1.
The far infrared vibrational exciton spectra of isotopic mixed crystals of naphthalene-h8 and d8 were studied. The two observed translational phonon modes were determined to fall into the amalgamated band limit while the lowest energy B3u, Au and B1u vibrational exciton bands were found to be in the separated band limit. The lowest energy B3u “butterfly” mode with its large (15 cm?1) exciton splitting was found to agree well with CPA calculations of mixed crystal spectra. A peak at 185 cm?1 was also assigned as a peak in the vibrational exciton density-of-states of the B3u mode.  相似文献   

2.
The librational modes of ferrocene-h10 and -d10 have been observed near 62 cm?1 (-h10) and 40, 52 and 60 cm?1 (-d10). The polarization measurements at low temperatures can give no useful information concerning the vibrational assignment until the low temperature crystal structure is completely determined.  相似文献   

3.
The results of detailed spectroscopic experiments on the lowest nπ* triplet state of p-benzoquinone-h4, -dh3, 2,6-d2h2, -d4 and -CH3 in mixed and isotopic mixed crystals are presented and analyzed. The origin of the lowest B1g (nπ*) singlet-triplet transition in p-benzoquinone-h4 (PBQ-h4) is shown to be induced by asymmetric isotopic substitution and the oscillator strength of this origin is seen to be accounted for by a corresponding decrease in intensity of a level 16.9 cm?1 higher in energy in the pure PBQ-h4 crystal. The combined oscillator strength of these close lying levels is measured and found to be almost independent of deuteration.These results are discussed in reference to the previously proposed double minimum potential model for the lowest nπ* triplet state in PBQ-h4 and the applicability for this model is critically examined.Optical absorption experiments on heavily doped isotopic mixed crystals of PBQ-h4 in PBQ-d4 show hydrogen (deuterium) bounding effects between translational inequivalent molecules to be primarily responsible for the observed cluster states. These hydrogen bounding effects also induce the electronic origin of the B1g (nπ*) triplet state in case of a translational inequivalent dimer.A detailed vibrational analysis of the phosphorescence spectrum of PBQ-h4 in a PBQ-d4 host crystal at 1.8 K is presented and it is shown that the unobserved origin of the B1g (nπ*) triplet state of PBQ-h4 is located at 18609 ± 1 cm?1 and that the inversion splitting in this lowest excited state amounts to 21 ± 1 cm?1 in this mixed crystal system. An isotope effect is study on the vibronic structure in the emission spectrum further indicates that the excited state structure of PBQ is isotope dependent.The observed large isotope effect on the ZFS parameters of the lowest triplet state of PBQ-h4 is demonstrated to be an intramolecular phenomenon and explained as an isotope dependent spin-orbit contribution to the ZI-S parameters, induced by localization of the nπ* excitation on oxygen.Finally the dynamics of energy migration in the dilute PBQ-h4 in PBQ-d4 isotopic mixed crystal is probed by concentration and temperature dependent phosphorescence intensity measurements and it is suggested that trap-exciton band communication effects are of importance in this system.  相似文献   

4.
The kinetics of OH(ν = 0) and OH(ν = 1) have been followed using pulsed photolysis of H2O or HNO3 to generate hydroxyl radicals, and time-resolved, laser-induced fluorescence to observe the rates of their subsequent removal in the presence of HCl or HBr. The experiments yield the following rate constants (cm3 molecule?1 s?1) at 298 ± 4 K: OH(ν = 0) + HCl: ko = (6.8 ± 0.25) × 10?13; OH(ν = 0) + HBr: ko = (11.2 ± 0.45) × 10?12; OH(ν = 1) + HCl: k1 = (9.7 ± 1.0) × 10?13; OH(gn = 1) + HBr; k1 = (8.1 ± 1.05) × 10?12 For OH(ν = 1), the measurements do not distinguish between loss by reaction and relaxation, and the fact that k1 > ko for HCl is tentatively attributed to relaxation, probably by near-resonant vibrational—vibrational energy transfer. Clearly, neither of these exothermic, low-activation-energy reactions is enhanced to any great extent, if at all, by vibrational excitation of the OH radical.ft]*|Present address: Battelle/Pacific Northwest Laboratories, P.O. Box 999, Richland, Washington 99352, USA.  相似文献   

5.
The fluorescence spectra of the mixed crystal system anthracene (A-h10)-perdeuteroanthracene (Ad10) have been studied over the full concentration range at temperatures between 1.6 and 77°K. There exists a collective (mixed) A-h10-A-d10 S1 exciton band at all concentrations, the lower edge of which represents the emitting level for the intrinsic fluorescence at low temperatures. This edge shifts from 25097 cm?1 in the neat A-h10 crystal to 25156 cm?1 in the neat A-d10 crystal. The edge position is a non-linear function of the mixed crystal concentration. From that one gets the “critical” distances Ucr+ = 92 cm?1 and Ucr? = 131 cm?1 between the molecular S1 levels of a guest and the host anthracene (non-deuterated or deuterated), using a formula given by Lifshitz. For the critical distance Ucr+ one finds just a bound guest state above the host band, and for Ucr?1 a bound guest state below the host band.The transition from the S1 band edge to the S0 ground state is always forbidden, in the same way as in the neat A-h10 crystal. Only transitions to levels of intramolecular and lattice vibrations of the ground state have been observed. At all concentrations the fluorescence transitions from the lower S1 band edge of the mixed crystal take place to the vibronic levels of both A-h10 and A-d10. The difference in the frequencies of equivalent intramolecular vibrations of A-h10 and A-d10 results in the appearance of vibronic doublets in the intrinsic fluorescence. The relative intensities of the two doublet components depend strongly on both concentration and temperature. This is due to the influence of quasi-resonance and exciton-superexchange upon the guest states inside the mixed exciton band.For all concentrations one observes two transitions originating from levels inside the S1 exciton band.  相似文献   

6.
Two bands appear for each CN stretching and nitro deformation vibration in the infrared and Raman spectra of m-dinitrobenzene and m-dinitrobenzene-d4. The 907 cm?1 bending mode in the vibrational spectra of m-dinitrobenzene undergo 30 cm?1 upward shift upon d4 substitution. A normal coordinate analysis pointed out that the 937 cm?1 bending and 727 cm?1 CN stretching vibrations as well as 18b CD in-plane deformation are mixed to a great extent. The other nitro bending mode undergo also an inverse isotopic effect (2 cm?1 upward shift) due to coupling with the 18a CD in-plane deformation vibration.  相似文献   

7.
The fluorescence spectra of the mixed crystal system anthracene (A-h10) - perdeuteroanthracene (A-d10) have been studied over the full concentration range at temperatures between 1.6 and 77 K. There exists an amalgamated A-h10 - A-d10 S1 exciton band at all concentrations. The intrinsic fluorescence starts from the lower edge this S1 band at low temperatures. The edge shifts with a non-linear dependence with increasing concentration from 25097 cm−1 in the neat A-h10 crystal to 25156 cm−1 in the neat A-d10 crystal. The transition from the S1 band edge to the S0 ground state is always forbidden. Only transitions to levels intramolecular and lattice vibrations of the ground state have been observed. The fluorescence transitions take place to vibrational levels of both A-h10 and A-d10. This leads to a doublet structure of the vibrational bands. Due to the influence of quasi-resonance and exciton-superexchange the transitions to A-h10 vibrational states at low temperatures are more probable than it would correspond to the A-h10 concentration. Using the concentration shift of the lower S1 band edge an approximative determination of the energy exchange integral square sum to Σ M2 = 9600 cm−2 ± 50% is possible.  相似文献   

8.
The phosphorescence spectra of the C6H6C6H5D1p-C6H4D2symp-C6H3D3, C6D6 and 13CC5D in a borazine host crystal are analyzed at high resolution. The spectral lines are sharp (~2 cm?1 wide) indicating that the impurity molecules occupy a unique site in the borazine lattice which is probably substitutional. The phonon sidebands are weak,giving clean, well-resolved spectra much like those of isotopic mixed crystals. In contrast, however, the crystal field effects on the ground state vibrational levels are much smaller than those found for isotopic mixed crystals. The gas-to-crystal shifts are very small, the vibrational degeneracies are not removed and orientational splittings are only observable for a few select vibrational levels. For most vibrational levels and for the derivation of selection rules one can asume the effective crystal site symmetry to be D3d. The data provide the first conclusive evidence that the splitting observed in the benzene phosphorescence spectrum results from a distortion of the molecule when excited to the zeroth vibrational level of the T1 state. Furthermore, the data suggest that the distortion is intrinsic in nature (i.e.,is not caused by the crystal field).  相似文献   

9.
Electronically controlled photon-echo relaxation measurements, using two nitrogen pumped dye-lasers, are reported for mixed crystals of pentacene-h14 and -d14 in p-terphenyl-h14 at 1.5 K. In dilute mixed crystals (ca. 10?8 M) the photon-echo lifetime is found to be exclusively determined by the fluorescence lifetime. Homogeneous linewidths of 7.1 and 5.9 MHz at 1.5 K are then calculated for the electronic origin of the 1B2u1A1g transition of pentacene-h14 and -d14 respectively. The decrease in photon-echo lifetime at higher guest concentrations (ca. 10?7 M) is ascribed to energy transfer between excited and neutral guest molecules.  相似文献   

10.
SCF closed shell calculations were performed to determine the equilibrium structure and vibrational frequencies of the O4 molecule by means of Payne's method and with the help of the molecule's symmetry coordinates. The equilibrium geometry corresponds to symmetry group D2d with R = 1.505 Å and h = 0.094 Å. The vibrational frequencies are: ν5(E) = 885.5 cm?1, ν3(B1) = 1051.9 cm?1, ν1(A1) = 1018.3 cm?1, ν4(B2) = 880.3 cm?1. The second vibrational coordinate (A1) corresponds to a double-well potential. The first vibrational levels were calculated by a variational method.  相似文献   

11.
The rates of relaxation of HCl(ν = 1) and DCl(ν = 1) by atomic oxygen have been determined between 196 and 400 K using the laser induced vibrational fluorescence method. The values of the rate constants, κ1,H and κ1,D, can be matched quite well by Arrhenius expressions: κ1,H = 6.2 × 10?12 exp (?1.05 kcal mole?1/RT) cm3 molecule?1 s?1 and κ1,D = 2.9 × 10?12 exp (?0.5 kcal mole?1/RT) cm3 molecule?1 s?1. The most likely explanation of the absolute and relative magnitudes of these rate constants appears to be that relaxation occurs as a result of non-adiabatic vibronic transitions during collisions.  相似文献   

12.
In a molecular beam the effects of vibrational pumping of SF63 = 948 cm?1) are studied, using a line-tunable cw CO2 laser. Intracavity spontaneous Raman scattering is used for analysis. For excitation in the collision regime (xE/D ≤ 1), a thermal redistribution of the ν3 excitation over all vibrational modes is found, together with an average absorption up to six photons per molecule. The infrared absorption profile shows a red-shift of 6 cm?1. For excitation in the relatively rare collision regime (xE/D ? 4), a structured non-thermal ν1 Raman spectrum is observed, especially in the case of seeded molecular beams (10% in He). The observed hot-band peaks can be explained in terms of single-photon absorptions and collision-induced near-resonant V-V energy transfer, leading to single, double and triple excitations of the ν3 mode. The value of Trot in the beam is found to influence sensitively the non-resonant energy-transfer rate [e.g. hν3(948 cm?1)+ΔEroth4 + ν6)(962 cm?1) relative to the near-resonant transfer rate (hν3 + hν3 → 2hν3 + 3.5 cm?1)].  相似文献   

13.
The metal ion distribution on the two metal sites of monoclinic Mn1?xCux(HCOO)2 · 2(H,D)2O mixed crystals are studied by infrared and Raman spectroscopic methods. The spectral regions 3 200–3 400 cm?1 (vOH), 2 875–2 990 cm?1 (vCH), 2 330–2 500 cm?1 (vOD of matrix isolated HDO molecules), 1 350–1 400 cm?1 (symmetric CO2 stretching modes), 570–950 cm?1 (H2O librations), and 490 cm?1 (M? O lattice modes) are mostly sensitive to the metal ions present. The frequency shifts of these bands with increasing content of copper show that Cu2+ prefers the M(1) site, coordinated by HCOO? only. The strengths of the hydrogen bonds increase on going from manganese to copper formate, due to the increased synergetic effect of Cu2+. Solubility and X-ray data of the mixed crystals are included. Irrespective of the same crystal structure, two series of mixed crystals are formed: eutonic area at 0.65 ≥ x ≥ 0.5.  相似文献   

14.
Laser Raman spectra of ferrocene crystal are recorded for the stable (orthorhombic) and metastable (triclinic) low-temperature phases, and the stable and undercooled (monoclinic) high-temperature phases.The skeletal vibrational modes [v4(A1g) and v16(E1g)], the CH bending (⊥e) mode [v25(E2g)], and the lattice modes below 100 cm?1 show characteristic changes among these phases.  相似文献   

15.
The Raman spectra of gaseous and liquid (SiH3)2NCH3 and (SiH3)2NCD3 have been recorded to within 10 cm?1 of the exciting line. The IR spectra of (SiH3)2NCH3 and (SiH3)2NCD3 have been recorded from 80 cm?1 to 3800 cm?1 in the gaseous state, and from 80 cm?1 to 450 cm?1 in the solid state. A vibrational assignment has been made, and from the low-frequency vibrational data, an upper limit of 3.3 kcal mol?1 was calculated for the barrier to internal rotation of the silyi groups, whereas a barrier of ~450 cal was calculated for internal rotation of the methyl group. It is concluded that there exists a significantly strong dπpπ interaction in methyldisilylamine.  相似文献   

16.
Polarized Zeeman absorption experiments on 9,10-anthraquinone crystals show the lowest triplet state in this molecule to be a g nπ* state. The gap between this state and the higher u nπ* state is found to be 410 cm?1. The phosphorescence spectrum of an isotopically mixed crystal of AQ-h8 in AQ-d8 is analyzed in detail and confirms the orbitally forbidden nature of the emitting state. The results are compared with those previously obtained for p-benzoquinone.  相似文献   

17.
The far infrared and Raman spectra of polycrystalline 1,2-dichloroethane and 1,2-dichloroethane-d4 for the low temperature modification have been measured from 450 to 33 cm−1 at various temperatures from −100 to −182°C. Raman spectra of the high temperature crystalline modification for both samples were also investigated. The Raman data are in conflict with those previously reported. Assignments are made for the lattice vibrations in terms of the crystallographic unit cell C2h5 (P21/c) with two molecules per unit cell. The spectra of the high temperature modification are consistent with those expected for orientationally disordered crystals.  相似文献   

18.
An optical Kerr shuttered spectrograph has been used to time resolve the spontaneous fluorescence of aromatic mixed crystal systems at low temperature with moderate resolution. Transient effects on the fluorescence of anthracene in naphthalene excited with 614 cm?1 vibrational excess energy in 1B2u have been observed that may signal measurable vibrational relaxation pathways. A model consistent with these observations is presented: it implicates a strong interaction between the intramolecular Franck—Condon and non-Franck—Condon modes in the relaxation process for specific excitation in the region of large excess lattice energy. Examination of the fluorescence for several aromatic systems integrated over the interval 0 to 30 ps following excitation high in the S1 vibrational manifold failed to reveal evidence of non-Boltzmann vibrational distributions, although other largely unexplained effects have been observed.  相似文献   

19.
Picosecond delayed CARS experiments on totally symmetric modes in naphthalene at 1.5 K are reported. The Raman lineshape of the vibrational excitons is lorentzian and vibrational relaxation can be surprisingly slow. The Raman lineshape of the Ag exciton level of the 766 cm?1 vibrational mode reveals that the low-temperature lorentzian lineshape occurs by motional narrowing At higher temperature the exciton is trapped by interaction with lattice phonons.  相似文献   

20.
Beryllium sulfide (BeS) in different forms from molecule, bulk, monolayer (h-BeS), to the single-walled nanotube obtained by wrapping the h-BeS monolayer along the (n,0) hexagonal lattice vector for n varying from n = 6 to 64, has been examined. Density functional theory (DFT) with an all electron basis set and the hybrid DFT/B3LYP level have been applied to compute energetic and geometrical, electronic and vibrational, elastic and piezoelectric properties, where the trend towards the hexagonal monolayer (h-BeS) in the limit of large tube radius is obtained. The vibrational properties including Raman spectra and polarizabilities are evaluated via the Coupled Perturbed Hartree–Fock and Kohn–Sham (CPHF/KS) computational schemes. For the first time, the IR vibrational modes at higher tube diameter and their convergence to the h-BeS monolayer limit are reported where the vibrational and electronic contributions to both perpendicular and parallel components of polarizability tensor are additionally discussed. For the (n,0) BeS nanotube family, three ranges of IR active phonon modes are determined. The first one located in the 0–300 cm−1frequency domain, goes regularly to zero when the tube diameter increases. Both the second (300–400 cm−1) and the third (700–800 cm−1) ones tend smoothly with different slope, towards the two optical vibrational modes of the h-BeS layer. These theoretical models can be extended to investigate further issues, such as the effect caused by the addition of a dopant, the influence of the substitutional fraction of nanotube atoms and the interaction of molecules outside and/or inside of the nanotube.  相似文献   

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