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  • 1
    Electronic Resource
    Electronic Resource
    Strong asymmetry induced ΔKa=3 transitions in the CH2 b˜ 1B1→a˜ 1A1 spectrum: A study by Fourier transform emission spectroscopy (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 7010-7012 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Dispersed fluorescence spectra of the CH2b˜ 1B1→a˜ 1A1'2116 band were recorded by Fourier transform emission spectroscopy for a series of rotational levels in the b˜1 B1 (0,160,0) state. Strong ΔKa=3 transitions were observed with their intensity increasing as J increases in the a˜ 1A1 (0,1,0) state. The observed intensities could be well reproduced by a calculation based on a rigid asymmetric rotor Hamiltonian, in which CH2 was assumed to be linear in the b˜ 1B1 state and bent in the a˜1A1 state. The calculation shows that the intensity of the ΔKa=3 transitions arises from the asymmetry of the a˜ 1A1 state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463209
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  • 2
    Electronic Resource
    Electronic Resource
    Isomeric structures and van der Waals vibrational frequencies of the glyoxal⋅Ar complexes. I. Fluorescence excitation spectroscopy (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 2703-2716 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: From the band shape and the concentration dependence of the peak intensity in the fluorescence excitation spectrum observed in a supersonic expansion of a He/Ar/glyoxal mixture near the 000A˜←X˜ band of glyoxal, it was found that the spectral features can be assigned to the following van der Waals complexes; (glyoxal)2⋅Ar, glyoxal⋅Ar2, (glyoxal)2, and three different isomers of glyoxal⋅Ar. The approximate structures of the three glyoxal⋅Ar isomers have been determined from rotational band contour analyses. In the electronic ground state, the Ar atom is either on the C2 axis 3.6 A(ring) above the glyoxal plane (the top isomer), in the HCCO gulf of the glyoxal plane 4.3 A(ring) away from the glyoxal center of mass (the side isomer), or in the HCO gulf of the glyoxal plane 4.8 A(ring) away from the glyoxal center of mass (the front isomer). As the glyoxal molecule is electronically excited to the A˜ 1A1 state, the Ar atom moves away from oxygen by more that 1 A(ring) for all three isomers. Excited van der Waals vibrational levels associated with the 0¯0, A˜ state of glyoxal were observed and assigned for all three glyoxal⋅Ar isomers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462018
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  • 3
    Electronic Resource
    Electronic Resource
    Vibration–rotation spectroscopy by stimulated emission pumping in a supersonic beam: a-Axis Coriolis coupled v4=1 and v8=1 levels of X˜ 1Ag glyoxal (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 2609-2614 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In combination with supersonic cooling, stimulated emission pumping (SEP) can be used to obtain vibrational spectra of medium-size molecules in their electronic ground state with single rotational level selectivity. The greatly reduced rotational congestion in the spectra of 0.04 cm−1 resolution makes the vibration–rotation assignment straightforward. Two vibrational levels, C–C stretching v4=1 with vibrational term values determined at 1065.80(1) cm−1 and CH wagging v8=1 at 1048.07(1) cm−1, of glyoxal were studied. These vibrational levels are symmetry forbidden in the IR spectroscopy, but can be detected by SEP. Their rotational constants are determined from primarily the low J, K levels, as A=1.9394(25), B=0.1594(25), and C=0.1426(25) cm−1 for 41 and A=1.7335(14), B=0.1594(10), and C=0.1464(8) cm−1 for 81. The A constants and the symmetries indicate that the two vibrational levels are strongly coupled to each other through the a-axis rotation. A deperturbation analysis yielded the A constants as 1.8414(126) for 41 and 1.8317(127) for 81, as well as the Coriolis coupling constant ζa48 =0.3642(226). These, and other previous observations, indicate that Coriolis interactions are important in promoting intramolecular vibrational relaxation in the glyoxal molecule.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455009
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  • 4
    Electronic Resource
    Electronic Resource
    Orientation and molecular orbital dependence in the spin changing collision C2H2O2(S1)+Ar→C2H2O2(T1)+Ar: A study through van der Waals complexes (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 711-714 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The orientation dependence in the spin-changing collision C2H2O2(S1)+Ar→C2H2O2(T1) +Ar has been examined by time-resolved laser induced fluorescence studies of the intersystem crossing rates in the glyoxal⋅Ar complexes with isomeric structures. Dramatic variation of intersystem crossing rates with complex structures and van der Waals excitations indicate strong orientation dependence in this process. Experimental results show that Ar interaction with the glyoxal n(O) orbital is two orders of magnitude more effective in inducing intersystem crossing than Ar interaction with the π* (CO) orbital.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463568
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  • 5
    Electronic Resource
    Electronic Resource
    Bending overtones and barrier height of a˜ 1A1 CH2 by flash photolysis stimulated emission pumping (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 4615-4623 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The J≤7 and Ka≤3 rotational levels of the bending vibrational overtones, (0,2,0), (0,3,0), and (0,4,0), and the (1,1,0) combination band of a˜ 1A1CH2 were characterized in detail by stimulated emission spectroscopy. The methylene was generated from ketene photolysis. Spectroscopic analyses using a rigid rotor Hamiltonian gave the vibrational term values and rotational constants. The latter were found to be strongly J and Ka dependent suggesting the inadequacy of the rigid rotor Hamiltonian for calculating the rotational energy to high accuracy. Effects of Coriolis, Fermi, and singlet–triplet perturbations were all observed in the spectra and discussed. Abnormally intense ΔKa=3 transitions were observed in the a˜←b˜, 2162 and 2163 bands. From fitting the experimentally measured bending vibrational term values by a model calculation based on the WKB theory, the barrier height to linearity in the a˜ state was determined to be 9870 cm−1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458701
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  • 6
    Electronic Resource
    Electronic Resource
    Transient vibrational spectroscopy by flash photolysis stimulated emission pumping: 3ν2 of singlet methylene (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 7033-7035 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A vibration–rotation spectroscopic method based on stimulated emission pumping has been developed for transient molecules generated by flash photolysis. This method may be generally applicable to radicals with electronic excited states accessible by visible or UV laser pulses. This first demonstration on the bending v2 =3 level of a˜ 1A1 CH2 generated a vibrational term value of 3950.45(7) cm−1 and the rotational constants A=25.665(40), B=11.470(7), and C=6.7140(61) cm−1. These constants indicate that the 3ν2 level is well below the bending-potential barrier. Perturbations of several rotational levels by the triplet state are identified. In addition, and most interestingly, abnormally intense ΔKa =3 transitions were observed in the a˜←b˜ 2163 band.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455331
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  • 7
    Electronic Resource
    Electronic Resource
    State-to-state rotational energy transfer and reaction with ketene of highly vibrationally excited b˜ 1B1 CH2 by time-resolved Fourier transform emission spectroscopy (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 6906-6916 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Dispersed fluorescence spectra from the CH2 b˜ 1B1→a˜ 1A1 band were recorded with time-resolution by Fourier transform emission spectroscopy after pulsed excitation of a single rotational level of the b˜ 1B1 (0,160,0) state. Fluorescence observed from the initially excited level and from levels populated by rotational energy changing collisions with the bath gas (ketene) was used to deduce the state-to-state rate constants for rotational energy transfer and the state-resolved rate constants for total collisional removal of b˜ 1B1 CH2. The observed propensity rules for rotational energy transfer—ΔJ=±2, ΔKa=0, and ΔKc=±2—are consistent with a quadrupole–dipole interaction between b˜ 1B1 (0,160,0) CH2 and ketene. The existence of a quadrupole in the intermolecular interaction suggests that the structure of CH2 in the b˜ 1B1 (0,160,0) state, averaged over the time of a collision, must be linear. The state-to-state rotational energy transfer rate constants range from approximately equal to the hard sphere gas kinetic rate to four times the gas kinetic rate, with the largest rate constants between rotational levels with the smallest energy gaps. Examination of fluorescence spectra recorded with polarization analysis shows that rotationally elastic (ΔJ=0)M changing collisions are negligible. State-resolved rate constants for reactive collisions between b˜ 1B1 CH2 and ketene were obtained by subtracting the rotational energy transfer contribution from the total rate constants for collisional removal of b˜ 1B1 CH2 (obtained from a Stern–Volmer analysis). These rate constants vary from one to five times the hard sphere gas kinetic rate, and increase with rotational energy for the levels studied. Their magnitudes show that CH2 is about two times as reactive in its b˜ 1B1 state than its a˜ 1A1 state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464780
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  • 8
    Electronic Resource
    Electronic Resource
    Fourier transform dispersed fluorescence spectroscopy: Observation of new vibrational levels in the 5000–8000 cm−1 region of a˜ 1A1 CH2 (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 2469-2472 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Dispersed fluorescence spectra from the CH2 b˜ 1B1 state to highly excited vibrational levels of the a˜ 1A1 state were recorded by a new technique, Fourier transform dispersed fluorescence spectroscopy. The spectra obtained clearly show the advantages of using a Fourier transform spectrometer for dispersing fluorescence, namely emission over a wide spectral range can be efficiently detected with high sensitivity and resolution. These advantages allow four new vibrational levels in the CH2 a˜ 1A1 state to be observed; the (2,0,0) and (0,5,0) vibrational overtones and the (1,2,0) and (1,3,0) combination bands. The vibrational term values for these levels are given, along with the harmonic frequencies and anharmonicities for the v1 and v2 modes. From the (0,5,0) term value an improved estimate of the barrier height to linearity in the CH2 a˜ 1A1 state is made.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464176
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  • 9
    Electronic Resource
    Electronic Resource
    Time-resolved Fourier transform spectroscopy with 0.25 cm−1 spectral and 〈10−7 s time resolution in the visible region (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 3261-3267 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The development of a new time-resolved Fourier transform spectrometer that is capable of 0.25 cm−1 spectral resolution and better than 10−7 s temporal resolution in the visible is reported. The time-resolved capability of the spectrometer is achieved by coupling a step-scan interferometer to a transient digitizer/laser system. The operation of the spectrometer is described in detail, and scattered light and laser-induced fluorescence spectra from an I2 gas cell are presented to demonstrate the temporal and spectral resolution of the spectrometer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143815
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  • 10
    Electronic Resource
    Electronic Resource
    Interfacing a transient digitizer to a step-scan Fourier transform spectrometer for nanosecond time resolved spectroscopy (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 18-22 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new signal processing and data acquisition system has been developed that allows a Fourier transform spectrometer to be interfaced to external transient digitizers for time-resolved spectroscopy. Time resolution is limited only by the transient digitizer and detection system response time. For the present system it is about 1 ns. The capabilities of this system are demonstrated with visible Fourier transform spectra of both scattered laser light and fluorescence from electronically excited NO2 gas. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149536
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