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  • 1
    Digitale Medien
    Digitale Medien
    Constant-ionic-state spectroscopy of high-v Rydberg states of molecular hydrogen (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 3038-3049 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The (X 2Σ+g)np Rydberg states converging to the X 2Σ+g, v+≥9 ionization thresholds of molecular hydrogen were excited by double-resonance excitation via the E,F 1Σ+g, v = 6 level. The energy region of interest (139 500–140 000 cm−1) included the X 2Σ+g, v+=9, N+=0–3 ionization thresholds as well as the energetic threshold for ion pair formation. The decay of the autoionizing Rydberg states was studied by both conventional and constant-ionic-state photoelectron spectrometry. The results support the Δv=minimum propensity rule for vibrational autoionization of Rydberg states with a high level of vibrational excitation. However, the relative intensities of the (X 2Σ+g)np, v'≥ 9 Rydberg series converging to different rotational levels of the ion are dramatically different from those for the analogous Rydberg series with v'≤2. In addition, the two-color photoelectron spectrum via the E,F 1Σg+, v=6 level shows considerable intensity in the v+=7 and 8 photoelectron bands both on and off resonance, in marked contrast with the single-color photoelectron spectrum obtained for the same intermediate levels. These observations may be due to the dependence of the transition dipole matrix elements on the internuclear distance and to the presence of doubly excited electronic states that cross the H2+ X 2Σ+g potential curve at a total energy close to that accessed by the two-color excitation scheme.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.463045
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  • 2
    Digitale Medien
    Digitale Medien
    Photoelectron spectroscopy from the A˜ 1Au state of acetylene: The bending vibrations of C2H+2 X 2Πu (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 6238-6248 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Photoelectron spectra are reported for one-photon resonant, two-photon ionization of acetylene via a number of vibronic levels of the A˜ 1Au state. Because the A˜ 1Au state is trans bent and the X 2Πu ground state of the ion is linear, ionization from the A˜ 1Au levels produces a long progression in the trans-bending vibration of the ion. The X 2Πu state is split by the Renner–Teller interaction along the trans-bending coordinate; the analysis of the photoelectron spectra allows the determination of the Renner–Teller parameters and leads to reassignments of the cis and trans-bending vibrations in earlier photoelectron studies.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.461570
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  • 3
    Digitale Medien
    Digitale Medien
    Alignment of the E,F 1Σ+g, v'E=1 state of H2 by two-photon excitation (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 4734-4739 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The alignment of the E,F 1Σ+g, vE=1 state of H2 produced by two-photon excitation from the X 1Σ+g, v‘=0 ground state was investigated using two different techniques. First, in a single-color experiment, photoelectron angular distributions were measured for the two-photon resonant, three-photon ionization of H2 via the Q(0) and Q(1) transitions to the E,F 1Σ+g, v'E=1 state. The photoelectron angular distributions are consistent with an unaligned E,F 1Σ+g, vE=1, J'=1 state. Second, in a two-color experiment, the photoionization spectra of several vibrationally autoionizing (X 2Σ+g)np, v=1 Rydberg states excited from the v'E=1, J'=1 level of the E,F 1Σ+g state were measured as a function of the relative polarizations of the pump and probe beams. The polarization dependence of the relative intensities of the P(1) and Q(1) transitions was used to determine the alignment of the E,F 1Σ+g, vE=1, J'=1 state produced by the pump laser. Consistent with the angular distribution measurements, the polarization results indicate that the populations in the M'=0 and M'=±1 levels of the E,F 1Σ+g, v'E=1, J'=1 state are equal, within the experimental uncertainty of 15%.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.457691
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  • 4
    Digitale Medien
    Digitale Medien
    Rotational autoionization of np Rydberg series of D2 (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 262-274 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Two-color resonantly enhanced multiphoton ionization combined with photoelectron spectroscopy was used to study rotational autoionization of np Rydberg states of D2 near the first ionization threshold. This work represents an extension of the study by O'Halloran et al. [J. Chem. Phys. 90, 930 (1989)] on the analogous states of H2. As in that work, one laser was used to excite a two-photon transition to the E,F 1Σ+g, v'=E0, J'=0–4 levels, and a second laser was used to probe single-photon transitions to the rotationally autoionized np Rydberg states converging to the X 2Σ+g, v+=0, N¯+=1–6 rotational levels of D+2. Of the five dipole-allowed Rydberg series converging to v+=0 excited from each intermediate J' level (J'≥2), two are allowed to rotationally autoionize in a coupling scheme that assumes ejection of pure p waves in the ionization process and singlet coupling of the spins of the ion core and the outgoing electron; members of these Rydberg series have large half-widths. As in H2, autoionization requiring the change of four quanta of rotational energy was found to be significantly slower than that requiring the minimum change of two quanta. Ionization was also observed for the series that are forbidden to rotationally autoionize according to this simple coupling scheme, and it is shown that both the inclusion of f waves in the autoionization process and singlet–triplet mixing may be required to explain these observations. By extending the wavelength region of the J'=4 spectrum beyond that of the earlier study on H2, rotational autoionization requiring even higher partial waves was observed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.458473
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  • 5
    Digitale Medien
    Digitale Medien
    Optical–optical double resonance studies of rotational autoionization of NO (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 2201-2212 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Optical–optical double resonance spectroscopy is used to probe Rydberg series converging to the first ten rotational levels of NO+ X 1Σ+, v+=0. Above the lowest ionization threshold, rotational autoionization of Rydberg series converging to higher thresholds is observed. Predissociation of these Rydberg states is found to compete with rotational autoionization in much the same manner as predissociation competes with vibrational autoionization in the region of the first few vibrational limits of NO+. The presence of this competing decay process, which has a decay rate similar to that of rotational autoionization, permits the comparison of rotational autoionization rates for different changes in rotational quantum number (ΔN+). Rotational autoionization by ΔN+=2 is found to be faster than by ΔN+=1 or 3. This results from the requirement that ΔN+=even processes require interactions between levels that both have even or both have odd values of orbital angular momentum l, while ΔN+=odd processes require interactions between levels of which one has even l and the other has odd l. In NO, the latter interactions are known to be quite weak. The electric field dependence and pressure dependence of the ionization threshold are also discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.456015
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  • 6
    Digitale Medien
    Digitale Medien
    Vibrational branching ratios following two-color excitation of autoionizing np Rydberg states of H2 (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 75-84 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Two-color resonantly enhanced multiphoton ionization-photoelectron spectroscopy (REMPI-PES) was used to determine vibrational branching ratios following autoionization of the ungerade npσ 1Σ+u and npπ 1Πu Rydberg states of H2. In this two-step experiment, one laser used to excite the two photon transition to the E,F 1Σ+g, v'=E2, J'=1 state, and a second laser was used to access the autoionizing Rydberg states near the H+2X 2Σ+g, v+=2 ionization limit. Electrons corresponding to the formation of H+2X 2Σ+g, v+=0 and 1 were collected and energy analyzed using a magnetic bottle electron spectrometer. In agreement with the well-known propensity rule for vibrational autoionization, the vibrational branching ratios strongly favor the final ionic state that corresponds to the minimum change in vibrational quantum number. In general, the branching ratio into the v+=1 channel is 94%–96%, while that into the v+=0 channel is 4%–6%; however, two major deviations from this trend were observed for Rydberg states that are perturbed by the 3pπ 1Πu, v=9 and 4pσ 1Σ+u, v=7 states. Although these low n/high v interlopers were not observed in the present work (since their ionization efficiency is near zero), interchannel coupling apparently causes their influence to be felt by nearby Rydberg states, resulting in v+=0 branching ratios as high as 18%. A number of additional studies suggested by these initial results are discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.455463
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  • 7
    Digitale Medien
    Digitale Medien
    Two photon spectra of electronic states of Kr2 and ArKr near the Kr* 4p55p states (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 4139-4146 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The two photon resonant, three photon ionization spectra of Kr2 and ArKr were determined in the energy region of the Kr* 5p[3/2]1, 5p[3/2]2, and 5p[1/2]0 states. The spectrum of Kr2 displays three new band systems that arise from two photon transitions from the ground state to excited states of gerade symmetry. The analysis of the observed vibronic structure of these band systems provides new information on the dissociation energies and the potential energy curves of the low-lying dipole forbidden excited gerade states of Kr2. A photoelectron spectrum determined following (2+1) excitation via an intense peak of the band system dissociating to Kr 1S0+Kr* 5p[1/2]0 provides the first observation of the weakly bound C 2Π3/2u state and the repulsive B 2Π1/2g and D 2Σ+1/2g states of Kr2. The (2+1) ionization spectra for both ArKr and KrXe were examined in the same energy region. For ArKr, a band system analogous to that observed in Kr2 was observed near the Kr* 5p[1/2]0 state, and an additional band system was observed near the Ar* 4s[3/2]01 state. No structure was observed for KrXe.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.454727
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  • 8
    Digitale Medien
    Digitale Medien
    Rotational state distributions from vibrational autoionization of H2 (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 6243-6253 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Optical–optical double-resonance excitation together with electron spectroscopy was used to measure the H+2 rotational state distributions produced by vibrational autoionization of singlet np Rydberg states of H2 . In the two-color excitation scheme, one laser was used to excite the two-photon transition to the H2 E, F 1∑+g, v'=1, J'=1 state, and a second laser was used to probe single-photon transitions to the vibrationally autoionized np Rydberg series converging to the X 2∑+g, v+=1, N¯+=1 and N¯+=3 levels of the ion. The expected P(1)npσ, Q(1)npπ, R(1)np1, and R(1)np3 Rydberg series converging to v+ =1 were observed and assigned, as were several interlopers converging to higher vibrational levels of the ion. Rotationally resolved photoelectron spectra were determined for all of the autoionizing transitions by using a magnetic bottle electron spectrometer. Under the normal assumptions that p waves are ejected and that spin effects are negligible, vibrational autoionization of the upper levels of the P(1)npσ and Q(1)npπ transitions should produce only v+ =0, N¯+ =1, while vibrational autoionization of the upper levels of the R(1)np1 and R(1)np3 transitions should produce a mixture of v+ =0, N¯+ =1 and v+ =0, N¯+ =3. Significant deviations from these expectations were observed. For example, vibrational autoionization of the upper levels of the Q(1)npπ transitions produced substantial amounts of v+ =0, N¯+ =3, while vibrational autoionization of the upper levels of certain Q(1)npπ, R(1)np1, and interloper transitions produced nonnegligible amounts of v+ =0, N¯+ =5. This indicates that vibrational autoionization of npπ Rydberg states is accompanied by rotational state changes in the H+2 core to an unexpected degree, and that additional mechanisms for exchange of angular momentum within the excited complex must be considered. Possible contributingmechanisms are critically assessed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.456341
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  • 9
    Digitale Medien
    Digitale Medien
    Two-photon spectroscopy of Rydberg states of molecular oxygen (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 3072-3084 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Two-photon resonant, three-photon ionization spectrum of O2X 3Σ−g, v‘=0 is presented in the energy region between the 5s–4d complex and the O+2X 2Π1/2g, v+=0 ionization threshold. The spectrum exhibits a number of new transitions to ns and nd Rydberg states with n=5-9 and v'=0 and 1 as well as transitions to the previously unobserved 5s–4d, v'=3 levels. For a given value of n and v', the observed bands split into two groups separated by approximately the O+2X 2Π1/2g−2Π3/2g spin–orbit splitting. All of the bands show at least some sharp rotational structure, although in most cases this structure is limited to a few lines. In addition, the direct two-photon ionization spectrum of O2X 3Σ−g, v‘=0 is presented in the energy region between the O+2X 2Π1/2g, v+=0 and 1 thresholds; the spectrum shows transitions to Rydberg states with n=8-12 and v'=1. These states are analogous to the v'=0 states observed below the ionization threshold, and they decay by vibrational autoionization into the v+=0 continuum. Taken together, the v'=0 and 1 Rydberg states observed here provide a significant addition to the knowledge of Rydberg series converging to the ground electronic state of O+2.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.458841
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  • 10
    Digitale Medien
    Digitale Medien
    Rotational state distributions from vibrational autoionization of H2 revisited (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 1831-1838 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Photoelectron spectra of vibrationally autoionized (X 2Σ+g)np, v=1,2 Rydberg states of H2 were obtained by using an optical–optical double-resonance technique. The spectra were obtained by using a hemispherical electrostatic electron energy analyzer that had sufficient resolution to determine the rotational state distributions of the H+2 ions. The ionization process occurred in a magnetic and electric field-free region. All of the results are consistent with the assumptions that the photoelectrons are ejected as p waves and that spin effects are negligible. This is in sharp contrast to our earlier results obtained by using a magnetic bottle electron spectrometer, in which the ionization process occurred in a 0.5–1.0 T magnetic field [J. L. Dehmer et al., J. Chem. Phys. 90, 6243 (1989)]. It is concluded that the magnetic field can significantly modify the rotational distributions observed for vibrational autoionization. The implications of this conclusion are discussed, with particular attention to other experiments performed with the magnetic bottle spectrometer.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.458065
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