摘要:

AbstractThe Raman (3100–10 cm−1) and infrared (3100–30 cm−1) spectra of acetyl isocyanate, CH3C(O)NCO, and the d3‐isotopomer were recorded for the gases and solids. Additionally, the Raman spectra of the liquids were recorded and qualitative depolarization values were obtained. The observed bands are assigned on the basis of the more stablecis (syn)conformer (isocyanate groupcisto the carbonyl bond) and less stabletrans (anti)conformer in the vapor state. ΔH of the gas is estimated to be 433 cm−1[1.24 kcal mol−1(1 kcal = 4.184 kJ)] from the relative intensity of the conformer pair at 800 and 763 cm−1. From the temperature dependence of the Raman spectrum of the liquid, two conformer pairs were used to determine experimentally a ΔH value of 370 ± 60 cm−1(1.06 ± 0.17 kcal mol−1) but now with thetransconformer the more stable form. In the annealed crystalline solid, only thetransconformer remains. The fundamental asymmetric torsion of thecisconformer was observed at 79 cm−1with two excited states falling to lower frequency. Utilizing these data and ΔH for the gas the potential function governing the conformer interchange was estimated. A complete vibrational assignment is proposed for both conformers based on infrared band contours, Raman depolarization data, group frequencies and normal coordinate calculations. The experimental confirmational stability, barriers to internal rotation and fundamental vibrational frequencies are compared with those obtained fromab initioHartree–Fock gradient calculations employing the RHF/6–31G* basis set and to the corresponding quantities obtai

ISSN:0377-0486    

DOI:10.1002/jrs.1250240502

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe Raman spectra of erythrocyte membranes in water and D2O were analyzed to determine the percentage of protein and lipid contributions to the amide I spectral feature. The approach of Lippertet al. [J. Am. Chem. Soc.98, 7075 (1976)] was modified to use circular dichroism data for protein conformations of erythrocyte membranes to determine the relative lipid and protein contributions to the 1660 cm−1spectral feature. It was determined that 69 ± 15% of the measured peak intensity was due to the protein contribution. The implication of this data to the quantity of α‐helix conformation in membrane protein of erythrocytes, and alternative approaches to determine protein conformation from Raman spectra are disc

ISSN:0377-0486    

DOI:10.1002/jrs.1250240503

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractFourier transform (FT) Raman spectroscopy is shown to be a very powerful and valuable technique for the analysis of brightly colored dyestuffs and pigments. The use of a near‐infrared Nd: YAG laser, as opposed to visible lasers used in conventional Raman instrumentation, virtually eliminates fluorescence from the dye, thus allowing high‐quality Raman spectra to be collected. The small amount of sample required and the limited sample preparation involved also make FT Raman spectroscopy attractive when the amount of sample available is limited or when a rapid, reliable analysis is needed. FT Raman spectra along with the complementary FT‐IR spectra of various commercially available dyestuffs and pigments are pres

ISSN:0377-0486    

DOI:10.1002/jrs.1250240504

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe far‐infrared spectrum (375–30 cm−1) of gaseous 2‐bromo‐3‐fluoropropene, CH2C(CH2F)Br, was recorded at a resolution of 0.10 cm−1. The fundamental asymmetric torsional mode is observed at 112.6 cm−1with four excited states falling to lower frequency for thes‐cis(fluorine atom eclipsing the doubel bond) conformer. For the higher energygaucheconformer, the asymmetric torsion is tentatively assigned to a very weak band at 93.0 cm−1. From these data the asymmetric torsional potential was calculated. The potential function coefficients are calculated to beV1= 306 ± 5,V2= −120 ± 4,V3= 928 ± 6,V4= 118 ± 2 andV6= 83 ± 2 cm−1, with an enthaply difference between the more stables‐cisand higher energygaucheconformers of 200 ± 30 cm−1[572 ± 86 kcal mol−1(1 kcal = 4.184 kJ)]. This function gives values of 1009 cm−1(2.88 kcal mole−1), 1024 cm−1(2.93 kcal mol−1) and 799 cm−1(2.88 kcal mol−1), for thes‐cistogauche, gauchetogauche, andgauchetos‐cisbarriers, respectively. From the relative intensities of the Raman lines of the gas at 548 cm−1(gauche) and 678 cm−1(s‐cis) as a function of temperature, the enthalpy difference is found to be 196 ± 23 cm−1(560 ± 66 cal mol−1), and a similar study of the liquid gives a value of 66 ± 4 cm−1(189 ± 11 cal mol−1) with thes‐cisconformer the more stable rotamer in both of these phases. Thes‐cisconformer is the rotamer present in the crystalline solid. The Raman spectrum of the gas was recorded from 3500 to 70 cm−1and, utilizing these data and previously reported infrared data, a complete vibrational analysis is proposed for both conformers. The conformational stability, barriers to internal rotation and fundamental vibrational frequencies, which were determined experimentally, are compared with those obtained fromab initiogradient calculations employing the RHF/LANL1DZ basis set and/or this basis set with electron correlation at t

ISSN:0377-0486    

DOI:10.1002/jrs.1250240505

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractRaman and infrared spectra of the very unstable compound 2,3‐diiodobuta‐1,3‐diene were recorded in the crystalline state at low temperatures in the spectral ranges 3300–10 and 4000–200 cm−1, respectively. Owing to a rapid polymerization rate at room temperature, only incomplete IR data were obtained of the sample in CCl4solution. The vibrational spectra were analysed and support a planaranticonformer present in the cyrstal. The vibrational assignments are presented, supported by force constant c

ISSN:0377-0486    

DOI:10.1002/jrs.1250240506

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe IR spectra of 2,2‐di(fluoromethyl)‐1,3‐difluoropropane were recorded in the vapour and liquid states and as a solute in solvents of different polarity. Additional IR spectra were obtained for plastic and crystalline solids at low temperature and at high pressure, and also of the compound isolated in argon and nitrogen matrices, using the hot nozzle technique. Corresponding Raman spectra of the liquid, of solutions and of the plastic phase were recorded at different temperatures in addition to the crystalline solid. There are six possible staggered conformations with symmetriesD2d,S4,C1*,C1,C2andCsin this molecule, and all but the last two were detected in the spectra. The two most stable conformers areS4andD2dwhich have no 1,3‐parallel CF interactions. Among themS4isca.0.5 and 1 kJ mol−1lower in energy thanD2din the plastic phase and in the matrices, respectively, andS4is present in the low‐temperature and high‐pressure crystals. A plastic phase, in which more conformers were present, was observed at temperatures belowTmeltand at high pressure. TheC1* andC1conformers both have enthalpies 5–10 kJ mol−1higher thanS4and their bands are enhanced at increased temperatures both in the plastic crystal and in the matrices. They have dipole moments around 2–3 D, and the intensities of their bands increase in polar solvents. The enthalpy differences ΔH° were calculated from variable‐temperature measurements in the plastic crystal and in the matrices, and confirmed by Gaussian 90 with basis sets 6–31G* and 6–31G and by semiempirical and molecular mechanics calculations: MNDO, AM1 and MM2. A nearly complete assignment of the fundamentals belonging toS4is presented. Additional bands are attributed to theD2d,C1* andC1conformers from annealing experiments at different temperatures in the N2matrix and in the amorphous phase. The assignments are based on the spectral observations and on the results of force constant calculations, involving s

ISSN:0377-0486    

DOI:10.1002/jrs.1250240507

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractResonance‐enhanced Raman scattering (RERS) from the groundX1Σg+(νg= 0,Jg) state of H2via the excited intermediateC1Πu(ν = 0/1/2/3,Ji) state coupled non‐adiabatically with theB1Σu+(νiB= 8/10/12/14,Ji) state was studied theoretically, applying second‐order perturbation theory. The excitation and Raman spectra for the pure rotational, fundamental and higher overtones are presented. Effects of non‐adiabatic coupling on the excitation profiles, scattered intensities and depolarization ratios were investigated. The intensities of excitation spectra and Raman lines forO‐,Q‐ andS‐branches were calculated using thermal Boltzmann factors for vibrational–rotational distribution at room temperature (300 K). The RERS cross‐sections with adiabatic and non‐adiabatic corrections are reported together with Born–Oppenheimer (BO) results where available, for comparison. The calculated RERS cross‐sections including non‐adiabatic effects were found to vary significant

ISSN:0377-0486    

DOI:10.1002/jrs.1250240508

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractChanges in the frequencies of the anisotropic and isotropic components of the OH bands in the Raman spectrum of aqueous, methanolic and ethanolic solutions of LiCl were investigated. With increased concentrations of LiCl a crossing of the components i.e. exchange of their positions, was observed, and the non‐coincidence values Δν = νaniso– νisoof the OH bands changed from positive to decidely negative. The results obtained suggest that some revision of existing theories of non‐coincidence is

ISSN:0377-0486    

DOI:10.1002/jrs.1250240509

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

ISSN:0377-0486    

DOI:10.1002/jrs.1250240501

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY