Molecule spectrum

Fleury L, Tamarat P, Kozankiewicz B, Orrit M, Lapouyade R and Bernard J 1996 Single-molecule spectra of an impurity found in n-hexadecane and polyethylene Mol. Cryst. Liq. Cryst. 283 81-7... 

G. Herzberg, Moleculer Spectra and Molecular Structure III. Electronic Spectra of Polyatomic Molecules, Van Nostrand, New York, 1967. 

Although we are mainly interested in adsorbed molecules, spectra often contain... 

R. L. Brown, L. Burnelle, M. A. A. Clyne, F. Kaufman and J. C. Polanyi have provided us with the results of their researches prior to publication. F. Kaufman and H. I. Schiff have aided with comments on parts of this paper. F. R. Gilmore, M. A. A. Clyne, E. A. Ogryzlo and B. A. Thrush have kindly provided figures. Professor Polanyi, the Chemical Kinetics Information Center (NBS), the Micro-wave Spectra Data Center (NBS) and the Diatomic Molecule Spectra and Energy Level Center (NBS) have supplied us with an abundance of reference material. The organization of the bibliography, tabular material and the typescript has been done by Mrs. M. C. Peter. To all of these we express our appreciation. 

Although we are mainly interested in adsorbed molecules, spectra often contain contributions from gas-phase species, and therefore some knowledge of gas-phase spectra is essential. Molecules in the gas phase have rotational freedom, and as a consequence the vibrational transitions are accompanied by rotational transitions. For a rigid rotor that vibrates as a harmonic oscillator, the expression for the available energy levels is ... 

Although some accurate work has been attempted for polyatomic molecules, the majority of published papers1 deals with diatomic molecules. This is not only for the reason that they are simpler but also because the level of understanding of diatomic molecule spectra is so much higher than that for polyatomic species. In the latter case relatively few spectra have been analysed to the level where all the rotational and fine structure is assigned. 

Parkin and Lopez-Delgado, where resolving powers of 750,000 were attained. However, the majority of large-molecule spectra have been recorded at resolving powers of less than the Doppler widths. 

The first optical absorption bands of benzene and pyridine are known to occur near 5 eV. The optical data on 1000 A thick, solution cast, PS and PVP as well as on the model molecules ethyl benzene and 2-ethyl pyridine in the gas phase were recorded on a Cary 14 double beam instrument. The data are therefore limited to >1 u <6 eV by the optics of the instrument. Condensed molecular solid spectra were not necessary since the photoemission studies had already shown that the polymer and condensed molecular spectra were equivalent. Therefore a comparison of gas-phase model-molecule spectra with that of the corresponding polymer spectra was sufficient. 

Single-molecule spectra as a function of laser intensity provided details of the incoherent saturation behavior and the influence of the dark triplet state dynamics [33]. Clear heterogeneity in the observed saturation intensity was observed indicating that the individual molecules experience modihcations in photophysical parameters due to differences in local environments. It was also possible to measure the linewidth of single pentacene molecules as a function of temperature in order to probe dephasing effects produced by coupling to a local phonon mode [33]. 

C. Hofmann, H. Michel, M. van Heel, J. Kohler, Multivariate analysis of single-molecule spectra Surpassing spectral diffusion. Phys. Rev. Lett. 94, 195501 (2005)... 

Apart from the (disordered and ordered) monolayer phases of tetraeene/ Ag(l 11), a second ordered phase is observed at higher coverage. This so-called (3-phase [69] is a bilayer with an extremely complex structure which is discussed elsewhere [49]. There are two notable facts about this phase. Firstly, the first layer of the bilayer is not the flat lying monolayer phase (a-phase). Rather, under the influence of the attractive intermolecular interactions with molecules in the seeond layer, the first layer re-orders and (partly) tilts up. This behaviour is markedly different from PTCDA, where the first layer forces the second layer into its epitaxial structure. This disparity indicates once more that for the two systems the weighting between intermolecular and interfacial interactions is different. Seeondly, a detailed analysis of single-molecule spectra in the (3-phase shows that the moleeular environment has a very strong influence on the electronic properties of individual molecules, even for molecules far away from the metal. 

Figure 1.13 Velocity Modulation Spectra (VMS). An AC electric field applied along the laser propagation direction causes the velocity, hence the Doppler shift, of ionic but not neutral species to be modulated. Spectrum (a) shows 127 MHz = 0.0042 cm-1 Doppler shifts of a 2479.4113 cm-1 ArH+ transition. Also shown is an Ar line that does not exhibit an electric field dependent Doppler shift. This spectrum was actually recorded at a fixed (DC) electric field using counter-propagating (frequency modulated) laser beams (from Haese, et ai, 1983). Spectrum (b) shows a portion of the VMS Nj A2 Hu — X2E (7,3) band. Since the AC electric field causes the Nj line to be frequency modulated, phase sensitive detection at the modulation frequency (If) results in a first derivative lineshape. Spectra (b) and (c) were recorded simultaneously. The Nj lines are absent from spectrum (c), which was recorded in population modulation mode by phase sensitive detection at twice the modulation frequency (2f). Spectrum (c) contains a few lines belonging to a N2 B3I19 — A3eJ First Positive baud. The population of N2 A3Ej is modulated at 2f because each half cycle of the AC field results in a full cycle modulation of the population of electronically excited N2 molecules. (Spectra (b) and (c) axe from Radunsky and Saykally, 1987.)...

The information contained in a diatomic molecule rotation-vibration-electronic wavefunction is enormous. But this is dwarfed by the information content of a time-evolving wavefunction that originates from a non-eigenstate pluck. A simplified, reduced-dimension representation, rather than an exact numerical description, is prerequisite to visualization and understanding. The concepts and techniques presented in this book, developed explicitly for diatomic molecule spectra and dynamics, are applicable to larger molecules. Indeed, any attempt... 

It is the early time dynamics, while the system remains highly localized in state space, the specific coupled states are known a priori, and the coupling matrix elements are experimentally measurable or theoretically predictable, for which our study of diatomic molecule spectra and dynamics prepares us. At early time, the system evolves in a reduced dimensionality. The excitation initially is localized spatially on a part of the molecule (a chromophore) and restricted by approximate constants of motion to a tiny fraction of energetically-accessible state space. 

Figure 15-7 Stopjsed-flow traces of iron oxidation by EcFtn-(E129K + E130A). Final protein concentration 3 pM in 0.1 M Mes buffer pH 6.5 and 48 Fe(II) atoms per molecule. Spectra recorded over 50 seconds using photodiode array stopped-flow spectrophotometer. Maximum absorbance at 600 nm was obtained at 0.9 seconds.

If it is desired to observe molecules in the unexcited state, which is really assumed only on absorption, attention must be directed to oscillation and rotation frequencies and work must be done in the infra-red region. Actually, the accurate study of infra-red absorption spectra of simple molecules in the gaseous state has contributed information which has proved very informative and important in the interpretation of molecule spectra, and in the knowledge of molecular structure. 

The first single-molecule spectra were recorded in the pentacene in p-terphenyl system in 1989 using a sophisticated zero-scattering-background absorption technique. 

Figure 6. The first single-molecule optical spectra, showing use of the FM/Stark technique for pentacene in />-terphenyl. (a) Simulation of absorption line with (power-broadened) linewidth of 65 MHz. (b) Simulation of FM spectrum for (a), com = 75 MHz. (c) Simulation of FM/Stark line-shape, (d) single-molecule spectra at 592.423 nm, 512 averages, 8 traces overlaid, bar shows value of 2o)m = 150 MHz. (e) Average of traces in (d) with fit to the in-focus molecule (smooth curve), (f) Signal far off line at 597.514 nm. (g) Traces of SFSatthe O2 line center, 592.186 nm. After Ref. 1.

Figure 10. Vibrationally resolved fluorescence spectra of terrylene in polyethylene (r= 1.4 K). Tlie bulk spectrum was obtained with excitation near the peak of the inhomogeneously broadened origin band. A-E represent spectra of different molecules which are described in the text. The average time to collect the single molecule spectra was several hundred seconds (from Ref. 38).

In the following, we restrict our discussion of single molecule spectra to the lowest temperatures, say below 5K. Therefore, the influence of matrix dynamics on the... 

Furthermore, the lowest doublet-doublet transitions, the positions of which are not shown in Fig. 12, are examples of very low-lying dipole-forbidden n n transitions. Specifically, the lowest bands are predicted to be at 5220 cm" (f= 0.001) and 7112cm" (f = 0.0007) for the Et-Chl-a and Et-BChl-a cation radicals, respectively. Thus, the present Ti-cation radicals appear to possess absorption spectra considerably more complex than those of the neutral parent molecules spectra not easily resolved experimentally or conveniently described by a siniple model. 

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