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  • 1
    Digitale Medien
    Digitale Medien
    Laser-induced fluorescence of the CD2CFO radical (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 6356-6362 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The laser-induced fluorescence spectrum of the B˜ 2A″→X˜ 2A″ transition of the CD2CFO radical has been observed in the region 316–335 nm. The radical was produced by 193 nm photolysis or by fluorine atom reaction with acetyl-d3 fluoride. The spectrum of CD2CFO was similar to that of CH2CFO reported previously except for small isotope shifts in the range 7–343 cm−1. The isotope shifts support the assignment of these spectra to fluorinated vinoxy radicals, and rule out the alternate assignment to FCO proposed by others. The X˜→B˜ electronic transition energy (T0) for CD2CFO was measured to be 29 867 cm−1, which is only 7 cm−1 lower than that for CH2CFO. From an analysis of the laser-induced single vibronic level fluorescence, some of the vibrational frequencies can be assigned for the ground electronic state; ν3(CO str.)=1735; ν4(CD2 sciss.)=1043; ν5(CF str.)=1248; ν6(CD2 rock.)=774; ν7(CC str.)=863; ν8(CCF bend)=597; and ν9(CCO bend)=370 cm−1. For the B˜ 2A″ state, ν3=1772; ν4=1073; ν5=1241; ν6=783; ν7=827; ν8=530; and ν9=370 cm−1. These assignments are supported by ab initio calculations. Among these fundamental frequencies, the ν4 and ν6 modes showed the largest isotope shifts, although isotope effects were observed in all the above vibrational fundamentals. The radiative lifetimes of the excited CD2CFO and the quantum yield of formation of the CH2CFO radical from photolysis of CH3CFO at 193 nm are also reported. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.479961
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  • 2
    Digitale Medien
    Digitale Medien
    Laser-induced fluorescence of radicals produced in reactions of halogenated ethylenes with atomic oxygen (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 6998-7000 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Three new laser-induced fluorescence spectra have been observed when reacting oxygen atoms with halogenated ethylenes such as CHFCF2, CF2CHCl, CH2CCl2, CH2CHCl, and CHClCHCl. These new spectra are similar to those reported previously for the vinoxy (CH2CHO) and CH2CFO radicals, which suggests that they can be assigned to other halogenated vinoxy-type radicals. Recently Williams and Fleming assigned one of these LIF spectra to the FCO radical; additional experiments have been done to address this conflicting assignment. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.474940
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  • 3
    Digitale Medien
    Digitale Medien
    Mechanisms and rate constants of the collisional deactivation of CO+(A 2Π,v) by He and Ar (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 6248-6256 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Collisional deactivation processes of CO+(A 2Π,v) by He and Ar are investigated in detail using both a time-resolved laser induced fluorescence and a threshold electron-secondary ion coincidence technique. Three deactivation mechanisms, pure vibrational relaxation, internal conversion, and charge transfer reaction, are identified. The time-resolved fluorescence from both the initially photoexcited and vibrationally relaxed levels of CO+ A 2Π makes clear the two distinct vibrational relaxation mechanisms: indirect two-step population of the lower levels in the CO+ (A)+He system and direct transition to the lower levels in the CO+(A)–Ar system. Threshold electron-secondary ion coincidence (TESICO) experiments demonstrate that the charge transfer reactions CO+ (A,v)+Ar→Ar++CO contribute significantly to the overall fluorescence quenching by Ar.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.464818
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  • 4
    Digitale Medien
    Digitale Medien
    Dissociation of doubly charged CH2=CD2 and CH2=CF2 in the region of valence shell photoexcitation (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 2908-2915 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Dissociative double photoionization of 1,1-dideuteroethene (CH2=CD2) and 1,1-difluoroethene (CH2=CF2) has been studied using the photoion–photoion coincidence (PIPICO) technique and monochromated synchrotron radiation over the photon energy range of 37–85 eV. PIPICO branching ratios and threshold energies for dissociative double photoionization show two dominant exit channels of the doubly charged ions (i) central C=C bond cleavage to form CXm++CYn+ fragment ions at a threshold below 37 eV photon energy. The decomposition into H++C2HD2+, D++C2H2D+, and F++C2H2F+ are also appreciable, and (ii) the fragmentation into H+(D+ or F+)+CXm+ takes place at hν(approximately-greater-than)37 eV. Comparison of the present PIPICO branching ratios with the recent theoretical studies of the electronic states of the outer valence doubly charged ethene ion [Liegener, Chem. Phys. 92, 97 (1985) and Ohrendorf et al., J. Chem. Phys. 91, 1734 (1989)] indicates that double ionization involving release of one πC=C electron results in central C=C bond breakage, while that of two electrons of the σCH, σCC, and C 2s orbitals of ethene forms two smaller fragment ions of the H++CXm+type.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.464118
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  • 5
    Digitale Medien
    Digitale Medien
    Negative-ion mass spectrometric study of ion-pair formation in the vacuum ultraviolet. II. OCS→S−+CO+, O−+CS+, and CO2→O−+CO+ (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 1710-1719 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Ion-pair formation from photoexcitation of OCS and CO2 has been studied by negative-ion mass spectrometry using synchrotron radiation in the 15–35 eV photon energy range. Negative ions S− and O− from OCS and O− from CO2 have been observed. The lowest onset energy in the photodissociation efficiency curve for each ion is in good agreement with the thermochemical threshold for the formation of the negative ion in the ground 2Pu state and its counterpart positive ion in the ground 2Σ+ state. There exist series of peaks with medium intensities in the efficiency curves of S− from OCS and O− from CO2; they are identified as resulting from predissociation of the Rydberg states converging to OCS+(B˜ 2Σ+) and CO+2(C˜ 2Σ+g), respectively. Broad peaks are observed at 18.4 eV (∼675 A(ring)) in the efficiency curves for both S− and O− produced from OCS. Predissociation of the excited valence state formed by the intravalence 9σ→10σ transition is considered to mainly contribute to these features. In addition, a broadband feature is present in the wavelength range of 400–620 A(ring) in the O− efficiency curve. The most likely candidate for the corresponding doorway state is the two-electron excited state involving simultaneous 9σ→10σ and 3π→4π transitions. In the case of the O− efficiency curve from CO2, two maxima observed at 21.4 (580 A(ring)) and 23.0 eV (538 A(ring)) are explained as resulting from the 3σu→5σg transition forming an excited valence state which effectively couples to the ion-pair continuum.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.459098
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  • 6
    Digitale Medien
    Digitale Medien
    Negative-ion mass spectrometric study of ion-pair formation in the vacuum ultraviolet. III. SF6→F−+SF+5 (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 8717-8724 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Ion-pair formation from photoexcitation of SF6 has been studied by negative-ion mass spectrometry using synchrotron radiation in the 11.27–31.0 eV photon energy range. Negative ions F−, SF−6, and SF−5 have been observed. The appearance energy of the F− ion is about 1 eV higher than the thermochemical threshold for the formation of the pair of the ground state ions F−(1Sg) and SF+5(X˜1A1). The peak features observed in the F− efficiency curve are interpreted as resulting from transitions to neutral excited states with the 1T1u symmetry which effectively couple with ion-pair states through avoided potential surface crossings. The peaks assigned to diffuse Rydberg states are distinctively enhanced in the F− efficiency curve, probably because of large transition probabilities from the dissociative Rydberg states to the ion-pair states. In contrast, the excited states of valence type autoionize in a short period and have quite small branching to the ion-pair channel. Consequently, the corresponding peaks are markedly suppressed in the F− spectrum. Assignments of the peak features in the previous photoabsorption spectra are also performed by using the term values for related Rydberg and virtual valence orbitals. Other negative ions observed, SF−6 and SF−5, are produced by resonance capture of low energy electrons emitted by photoionization of the parent molecules, and are not of major concern of the present study.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.459259
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  • 7
    Digitale Medien
    Digitale Medien
    Negative-ion mass spectrometric study of ion pair formation in the vacuum ultraviolet. I. N2O→O−+N+2 (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 6556-6560 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Negative ion formation from N2O has been studied using synchrotron radiation in the 15–40 eV photon energy range. Only O− ion signal is observed by mass spectrometry. The onset of the photodissociation efficiency curve for O− from N2O is in good agreement with the thermochemical threshold of 15.79 eV for the formation of O−(2Pu)+N+2(X˜ 2∑+g). Several series of peaks are identified as resulting from predissociation from the Rydberg states converging to N2O+(A˜ 2∑+, B˜ 2∏, and C˜ 2∑+). In particular, two Rydberg series (ndσ and ndπ) converging to the C˜ state are observed most prominently.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.458291
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  • 8
    Digitale Medien
    Digitale Medien
    Negative-ion mass spectrometric study of ion-pair formation in the vacuum ultraviolet. VI. CH3X→X−+CH+3 (X=F, Cl, Br) (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 7500-7505 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Ion-pair formation from photoexcited halomethanes, CH3X*→X−+CH+3 (X=F, Cl, Br) has been studied by measuring photodissociation efficiency curves of X− using synchrotron radiation in the 9.9–27.5 eV photon energy range. A new spectral feature is observed in each of the curves near the threshold for the removal of an na1 electron from CH3X (n=4, 6, and 8, respectively, for CH3F, CH3Cl, and CH3Br ). This feature, composed of two or three peaks in each case, is interpreted as resulting from photoexcitation to the Rydberg states converging to CH3X+(C˜ 2A1), which then predissociate into ion pairs through avoided potential energy surface crossings. The interpretation is based on the results of the inner-shell electron energy loss study by Brion and co-workers and the photoabsorption study by Hochmann and co-workers. Peak features are also observed in the X− efficiency curves near the ionization threshold for CH3X+(X˜ 2E). The origins of these peaks are also discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.462401
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  • 9
    Digitale Medien
    Digitale Medien
    Negative-ion mass spectrometric study of ion-pair formation in the vacuum ultraviolet. V. CF4→F−+CF+3 (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 2398-2406 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Ion-pair formation from photoexcitation of CF4 has been studied by negative-ion mass spectrometry using synchrotron radiation in the 11–31 eV photon energy range. Negative F− ions have been observed. The appearance energy in the F− photodissociation efficiency curve is about 2 eV higher than the thermochemical threshold for the formation of the ground-state ions F−(1Sg) and CF+3(X˜ 1A'1). The peak features observed in the spectrum are interpreted as resulting from transitions to Rydberg states with the 1T2 symmetry. Assignments of the peaks have been made on the basis of the previous work on photoabsorption cross-section curves of CF4. Repulsive Rydberg states converging to CF+4(X˜ 2T1, A˜ 2T2) give the strong and broad peaks in the F− efficiency curve. Conversion to the ion-pair state is considered to occur through the avoided potential surface crossings along the dissociation coordinate of the CF3—F bond. In contrast, the npt2 Rydberg states (n≥4) converging to CF+4(C˜ 2T2) show long vibrational progressions. The radiative and nonradiative decay pathways for these Rydberg states are discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.461782
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  • 10
    Digitale Medien
    Digitale Medien
    Negative-ion mass spectrometric study of ion-pair formation in the vacuum ultraviolet. IV. CH4→H−+CH+3 and CD4→D−+CD+3 (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 6003-6006 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Ion-pair formation from photoexcited methanes, CH@B|4 →H− +CH+3 and CD*4 →D− +CD+3, has been studied by measuring the efficiency curves of H− and D− using synchrotron radiation. Ion pairs are produced both by direct dissociation and predissociation of the npt2 (n=3–5) Rydberg state converging to the A˜ 2A1 state of CH+4/ CD+4. The 4pt2 and 5pt2 Rydberg states are observed here for the first time.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.460435
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