ISSN:0377-0486    

DOI:10.1002/jrs.1250211202

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractRecent experimental and theoretical developments in spontaneous hyper‐Raman spectroscopy (HRS) are reported. The scope of the general review of HRS presented summarizes the results of this non‐linear scattering technique during the past 10 years. In particular, those aspects of HRS studies which allow novel observations as compared with other spectroscopic techniques are emphasized. HRS investigations of crystals, liquids and surface and electronic resonance enhancement are highligh

ISSN:0377-0486    

DOI:10.1002/jrs.1250211203

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe resolution in the Raman spectra of gases has been greatly improved by the development of the different methods of non‐linear Raman scattering. When two laser beams, one of which has a tunable frequency, are focused in a sample, a stimulated Raman process occurs as soon as the frequency difference between the two lasers is equal to a Raman‐active rovibrational or rotational transition frequency. The Raman resonance can be detected in different ways: by coherent anti‐Stokes Raman scattering (CARS) or the corresponding Stokes process (CSRS), by a gain in one of the beams (stimulated Raman gain spectroscopy, SRGS) or a loss in the other (inverse Raman spectroscopy, IRS), or even by detection of a photoacoustic signal (photoacoustic Raman spectroscopy, PARS). The selective ionization of the excited molecules by a third ultraviolet laser (ionization‐detected stimulated Raman scattering, IDSRS) has considerably increased the sensitivity in special cases.The instrumental resolution is determined by the convoluted line widths of the lasers used for excitation. The narrowest line widths can be achieved with stabilized continuous‐wave lasers. Their relatively low power has been compensated for either by intracavity excitation of CARS spectra or by injection locking of dye laser amplifiers which are pumped by pulsed lasers or by flashlamps. Examples of investigations of the structure of rovibrational bands and of line‐width measurements as a function of pressure a

ISSN:0377-0486    

DOI:10.1002/jrs.1250211204

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractA theory of three‐photon (hyper‐Raman and hyper‐Rayleigh) scattering is proposed using the approach of irreducible Cartesian and spherical tensors. A general expression for the intensity‐time correlation function of symmetric, non‐symmetric and symmetric‐non‐symmetric three‐photon scattering is derived in terms of separated, irreducible field‐and molecular‐rotational invariants. The occurrence of the various types of scattering is dependent on the physical conditions, i.e. on the molecular symmetry and the ratio of the light frequency and molecular frequency. The (general) number of five irreducible molecular‐rotation and field invariants can undergo a reduction under appropriately chosen experimental and model conditions. The expressions for the intensity function hold for arbitrary (e.g. elliptical) states of light Polarization and angulardistributions. In particular, they are applied to linear and circular polarization. On their basis, equations are derived for the depolarization ratio and reversal coefficient of hyper‐Raman and hy

ISSN:0377-0486    

DOI:10.1002/jrs.1250211205

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractPicosecond‐excited surface‐enhanced hyper‐Raman scattering (SEHRS) spectra have been obtained for several non‐centrosymmetric oxa‐ and thia‐carbocyanine molecules adsorbed on pre‐aggregated colloidal silver. To facilitate interpretation of the SEHRS results, a comprehensive vibrational study of these dyes by employing Fourier transform (FT) IR spectroscopy, surface‐enhanced Raman scattering (SERS) and the newly developed techniques of near‐IR‐excited FT‐Raman and FTSERS is also reported. The SERS spectra of these carbocyanine dyes are dramatically different from their bulk FT‐Raman and SERS spectra, but exhibit similarities to their FTIR spectra. Many SEHRS lines appear to arise from vibrational modes of the central π‐conjugated chain, in contrast to the appearance of predominantly end‐chromophore vibrations in the Raman spectra. Some of the intense surface hyper‐Raman lines are found to be experimentally undetected or unresolvable by Raman scattering and IR absorption. The results thus conclusively demonstrate that, for non‐centrosymmetric molecules, surface‐enhanced hyper‐Raman scattering is capable of providing important vibrational information that is unobt

ISSN:0377-0486    

DOI:10.1002/jrs.1250211206

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractSelf‐broadened widths of28SiH4in the ν1Q‐branch have been measured at room temperature (295 K) using high‐resolution stimulated Raman Spectroscopy. These collisional widths have been obtained by fitting a super‐position of Voigt profiles to the experimental spectra in the pressure range 28–154 Torr. No evidence for line mixing within the tetrahedral components of aQ(J) line has been found. The line broadening coefficients forJup to 13 depend weakly on the rotational quantum number. The mean value is 103.7 × 10

ISSN:0377-0486    

DOI:10.1002/jrs.1250211207

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractNitrogen spectra of theQ‐branch of the fundamental and the first hot bands were recorde with a high‐resolution stimulated Raman spectrometer at atmospheric pressure andca.1300 K. The absolute frequencies of the Raman lines were measured with high accuracy, leading to a refinement of spectroscopic constants. A temperature estimation was also performed from the Raman intensit

ISSN:0377-0486    

DOI:10.1002/jrs.1250211208

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractHyper‐Raman scattering by the zone‐centre optical phonons of alkali metal halides is described in terms of an anharmonic shell model. In order to reproduce the measured relative values of the hyper‐Raman tensor elements, three types of fourth‐order coupling parameters, representing intra‐ionic, inter‐ionic and Coulomb anharmonicities have to be taken into account. Deducing the non‐linear force constants of the short‐range inter‐ionic interactions from a Born‐Mayer potential and supplementing them by exact expressions of their Coulomb Counterparts, it is possible to determine all parameters contributing to hyper‐Raman scattering. The model also predicts the third‐harmonic generation coefficients in satisfactory agreement

ISSN:0377-0486    

DOI:10.1002/jrs.1250211209

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractPure rotational coherent anti‐Stokes Raman spectroscopy using a single broad‐band dye laser was applied to study the rotational energy distribution of molecules in a pulsed supersonic beam. The multiplex BOXCARS configuration allows the accurate determination of rotational constants and rotational temperatures, and offers many advantages over other methods. The technique was applied to calibrate the cooling effect of a pulsed molecular beam of nitrogen and to study the rotational energy distributions of infrared multiphoton‐excited eth

ISSN:0377-0486    

DOI:10.1002/jrs.1250211210

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractExperiments in Raman amplification spectroscopy monitor the intensity change of one laser beam under the perturbing influence of another in a Raman‐active medium. Accompanying such changes one frequently observes the presence of other, non‐Raman, processes arising from non‐linear susceptibility terms χ(2)and χ(3), in addition to linear changes caused by species absorption and fluorescence. One such non‐Raman process observed during a Raman study of potassium dihydrogenphosphate (KDP) is sum‐frequency generation. Although the subject of second‐harmonic/sum‐and difference‐frequency generation is well understood, the indirect quantitative measurement of such processes by means of the measured power loss of one or other of the incident beams has remained an area hitherto unexplored. This paper redresses this omission by comparing experimentally the directly measured sum‐frequency power generated in a KDP frequency‐doubling crystal with the power loss of the probe beam transmitted through the crystal.The results, viewed in an overall perspective, are very promising and the experiments demonstrate the value of the pump‐probe technique as a means of investigating non‐linear optical mixing processes, with the added advantage of an experimental set‐up which may be adapted, with the minimum of adjustments, to accommodate simultaneous investigations of several other spectroscopic processes occurring within the same system. These studies provide an interesting and important route for the further understanding and utilization of the non‐linear processes occurring in

ISSN:0377-0486    

DOI:10.1002/jrs.1250211211

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY