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  • 1
    Electronic Resource
    Electronic Resource
    The H–NCS bond energy, ΔH(open circle)f (HNCS), ΔH(open circle)f (NCS), and IP(NCS) from photoionization mass spectrometric studies of HNCS, NCS, and (NCS)2 (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 7975-7989 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The species HNCS and NCS have been studied by photoionization mass spectroscopy. The adiabatic ionization potential (IP) of HNCS is ≤9.92 eV; the shape of the ion yield curve near threshold implies a large change in geometry, perhaps to linear HNCS+. Various appearance potentials (AP) from HNCS are determined by a more objective procedure, from which ΔH(open circle)f(HNCS)(approximately-greater-than)29.6 kcal/mol (and very likely ≥31.0±0.7 kcal/mol) is deduced. The adiabatic IP of NCS is 10.689±0.005 eV. This quantity, together with AP(NCS+/HNCS), yields D0(H–NCS)≤97.2±0.2 kcal/mol. However, a measurement of the appearance potential of NCS+ from (NCS)2 results in a still lower value, D0(H–NCS)≤93.3±1.1 kcal/mol, and ΔHf0(open circle)(NCS) ≤ 72.7 ± 0.8 kcal/mol. Approximate values are obtained for ΔHf0(open circle)(HNCS+) and for the proton affinity of NCS.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468495
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  • 2
    Electronic Resource
    Electronic Resource
    Threshold photoelectron spectrum of HOBr (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 9215-9218 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The threshold photoelectron spectrum (TPES) of HOBr has been obtained in the wavelength regions corresponding to the first and second ionization bands. The adiabatic ionization potential (IP) is 10.642±0.005 eV; the O–Br stretching frequency in this X 2A‘ state is found to be 730±20 cm−1. The adiabatic IP for the first excited state (A 2A') of HOBr+ is 11.448±0.005 eV. The latter value confirms an earlier, tentative conclusion based on the interpretation of autoionizing structure in the photoionization mass spectrum (PIMS). There is a slight difference in the TPES and PIMS values of the first adiabatic IP, whose origin is still somewhat ambiguous. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468012
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  • 3
    Electronic Resource
    Electronic Resource
    A photoionization study of the vinyl radical (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 7396-7404 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The photoionization spectrum of vinyl radical is reported, from its observed threshold to 1160 A(ring). Two methods of preparation have been employed; (a) the abstraction reaction of F atoms with C2H4, and (b) the pyrolysis of divinyl mercury at 1200 K. In both experiments, relatively sharp autoionization structure is observed, and interpreted as a Rydberg series converging to the excited 3A‘ state of vinyl cation. The analysis leads to an adiabatic ionization energy of ∼10.7 eV for this state, with a structure similar to that of vinyl radical but with an increased C–C distance. The observed ionization threshold for the ground state of vinyl cation is 8.59±0.03 eV with the F atom reaction, and 8.43±0.03 eV with the pyrolysis method. The lower value in the latter experiment is interpreted as a hot band. The relatively low value of the photoionization cross section near threshold implies a large geometry change between vinyl radical and ground state vinyl cation. A progression in the in-plane C–H bending vibration is indicated in the photoionization spectrum; it is quite possible that the vibrational 0–0 transition lies one quantum lower than our detected limit. With this bracketed adiabatic ionization potential and the appearance potential of C2H+3 (C2H4), a C–H bond energy in ethylene of 107–110 kcal/mol (0 K) is deduced.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454352
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  • 4
    Electronic Resource
    Electronic Resource
    Photoionization mass spectrometric studies of SiHn (n=1–4) (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 1235-1248 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A photoionization mass spectrometric study of SiH4 at T=150 K reveals the presence of SiH+4 with an adiabatic threshold at 11.00±0.02 eV. The implications for the structure of this Jahn–Teller split state are discussed. The appearance potentials of SiH+2 and SiH+3 are 11.54±0.01 eV and ≤12.086 eV, respectively. The reaction of F atoms with SiH4 generates SiH3 (X 2A1), SiH2 (X 1A1 and a 3B1), and SiH (X 2Π) in sufficient abundance for photoionization studies. The measured adiabatic ionization potentials (eV) are: SiH3, 8.01±0.02; SiH2 (X 1A1), 9.15±0.02 or 9.02±0.02; SiH2 (a 3B1), 8.244±0.025; SiH, 7.91±0.01. The singlet–triplet splitting in SiH2 is either 0.78±0.03 or 0.91±0.03 eV. The dissociation energy of SiH is 2.98±0.03 eV. A Rydberg series is observed, converging to SiH+ (a 3Π) at 10.21±0.01 eV. Heats of formation of the various neutral and ionic species are presented, as are the stepwise bond energies of SiH4.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452213
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  • 5
    Electronic Resource
    Electronic Resource
    The ionization potentials of CH4 and CD4 (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 674-676 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The adiabatic ionization potential of CD4 is measured by photoionization mass spectrometry to be 12.658±0.015 eV, which is 0.05±0.02 eV higher than that of CH4. The difference is attributed to zero point energy differences, rather than different Jahn–Teller stabilization energies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452268
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  • 6
    Electronic Resource
    Electronic Resource
    Determination of consecutive bond energies by photoionization of SbHn (n=1–3) (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 5840-5848 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A photoionization mass spectrometric study of SbH3 is presented. The adiabatic ionization potential (IP) of SbH3 is ≤9.40±0.02 eV. The lowest energy fragment ion, SbH+ (+H2), has an appearance potential (0 K) of 9.730±0.008 eV, while SbH2+ has an AP of 11.66±0.02 eV. The transient species SbH2 and SbH are generated in situ by reacting F atoms with SbH3. The IP of SbH2, forming SbH2+ (X 1A1), is 8.731±0.012 eV. The IP of SbH (X 3Σ−,0+) to form SbH+ (X 2Π1/2) is probably 8.753±0.009 eV, but certainly 〈8.79 eV. Autoionizing structure in the photoion yield curve of SbH+ (SbH) is interpreted as Rydberg series converging to SbH+ (a 4Σ−), which appears to be split into 1/2 and 3/2 components, with IP's of 10.843±0.011 eV and 10.866±0.011 eV. The difference in IP's (Sb–SbH, SbH–SbH2) appears to conform to the extended Goddard–Harding model, when adjusted for spin–orbit splittings. The derived heats of formation are ΔHf00(SbH)=59.1±0.3 kcal/mol and ΔHf00(SbH2)=52.5±0.6 kcal/mol. These values lead to D0(SbH)=56.4±1.0, D0(HSb–H)=58.3±0.6, D0(H2Sb–H)=67.5±0.5 (in kcal/mol). The differences in successive bond energies, 1.9±1.2 and 9.2±0.8 kcal/mol, depart significantly from the constant value (4.44 kcal/mol) predicted by the Goddard–Harding model. A rationalization is presented, that incorporates relativistic effects. This relativistic picture implies that for BiHn, D0(BiH)(approximately-greater-than)D0(HBi–H), a conclusion for which some experimental evidence exists. However, relativistic ab initio calculations, which agree rather well in their calculated differences in successive bond energies for SbHn, do not predict this reversal in BiHn.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465937
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  • 7
    Electronic Resource
    Electronic Resource
    Photoionization mass spectrometric studies of Sb2 and Bi2 (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 8445-8450 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The photoion yield curves of Sb+2(Sb2) and Bi+2(Bi2) are presented. In both cases, two autoionizing series (designated pσ and pπ) are observed, converging on the excited 2Σ+g state. From this information, the ionization energy of the 2Σ+g state in Sb2 is lowered to 9.247 eV. The difference in quantum defects, δpπ−δpσ, is shown to be related to the quadrupole moment of the molecular ion core of the A 2Σ+g state in Pn+2. The adiabatic ionization energies (AIP) are also decreased: AIP(Sb2)≤8.43 eV, AIP(Bi2)(approximately-less-than)7.34 eV. Although the uppermost occupied orbital is nominally a bonding pπ orbital, an analysis leads to the surprising conclusion that D0(Pn+2)(approximately-greater-than)D0(Pn2), where Pn=P, As, Sb, and Bi.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465620
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  • 8
    Electronic Resource
    Electronic Resource
    Photoionization mass spectrometry of CH2S and HCS (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 2568-2579 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The transient species CH2S and HCS were studied by photoionization mass spectrometry. They were prepared in situ from CH3SH by sequential hydrogen abstraction with fluorine atoms. CH2S was also prepared by pyrolysis of CH3SCl and CH3SSCH3. The photoion yield curve of CH2S displays an abrupt threshold, and is similar in overall shape to that of the homologue CH2O. The adiabatic ionization potential of CH2S is found to be 9.376±0.003 eV. Evidence has been found for nd and/or ns and np Rydberg states converging to the first excited state of CH2S+. In addition, the HCS+ fragment from CH2S has been determined to appear at ≤11.533±0.021 eV at 0 K. In contrast to CH2S, the photoion yield curve of HCS+ from HCS displays a very broad Franck–Condon envelope, consistent with a transition from bent HCS to linear HCS+. A Poisson fit to the experimental Franck–Condon factors indicates that the adiabatic ionization potential of HCS is ≤7.499±0.005 eV, and perhaps as low as 7.412±0.007 eV. The fragment curves at m/e=46, 47, 48, and 49 from CH3SSCH3 have also been examined, and their relative shifts in energy determined. Together with measurements on CH2S and HCS, and the previously reported ΔH(open circle)f0 (CH2SH+)=211.5±2.0 kcal/mol (≤213.1±0.2 kcal/mol), this is sufficient to establish ΔH(open circle)f0 (CH2S)=28.3±2.0 kcal/mol (≤29.9±0.9 kcal/mol) and ΔH(open circle)f0 (HCS)=71.7±2.0 kcal/mol (≤73.3±1.0 kcal/mol), ≥69.7±2.0 kcal/mol). These values are in very good agreement with recent ab initio calculations. The implications for various bond energies within the CHnS system are also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464139
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  • 9
    Electronic Resource
    Electronic Resource
    Photoionization mass spectrometric studies of the isomeric transient species CD2OH and CD3O (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 4033-4039 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Both CD2OH and CD3O were prepared in situ by the reaction of F atoms with CD3OH, and studied by photoionization mass spectrometry. The adiabatic ionization potential (I.P.) of CD2OH was found to be 7.540±0.006 eV, in good agreement with the photoelectron spectroscopy (PES) value, 7.55±0.01 eV. However, the adiabatic I.P. of CD3O was determined to be 10.726±0.008 eV, in marked contrast to the PES value for CH3O, 7.37±0.03 eV, but in the expected range based on reported values of ΔH0f(CH3O+) and ΔH0f(CH3O). From selected values of ΔH0f0(CH2OH+) ≤172.0±0.7 kcal/mol and ΔH0f0(CH3O) =5.9±1.0 kcal/mol, we deduce ΔH0f0(CH2OH) ≤−2.1±0.7 kcal/mol and ΔH0f0(CH3O+) =253.1±1.0 kcal/mol.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460758
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  • 10
    Electronic Resource
    Electronic Resource
    Photoion-pair formation and photoelectron-induced dissociative attachment in C2H2: D0(HCC–H) (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 5586-5593 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The formation of C2H− is observed in two broad resonance bands when C2H2 is irradiated with vuv light. The higher-energy band has partially resolved structure, approximately linear pressure dependence, and a threshold at 16.335±0.021 eV. It is attributed to photoion-pair formation (C2H−+H+) consequent upon predissociation of one or more Rydberg states. This threshold, together with IP(H) and EA(C2H), gives D0(HCC–H)≤5.706±0.022 eV≡131.6±0.5 kcal/mol, or ΔH0f0 (C2H)≤134.5±0.5 kcal/mol. The lower-energy band has an approximately quadratic pressure dependence and curved step-like structure. It is attributed to photoelectron-induced dissociative attachment mediated by a πg shape resonance. The threshold, at 878.5±2.0 A(ring), corresponds to a photoelectron energy of 2.715±0.032 eV. This threshold combined with EA(C2H)=2.969±0.010 eV, yields D0(HCC–H)≤5.684±0.033 eV≡131.1±0.7 kcal/mol, or ΔH0f0 (C2H)=134.0±0.7 kcal/mol.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459629
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