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Photoelectron velocity map imaging is combined with one- and two-photon ionization to study the near threshold photoionization of the 2-butyne molecule. In this region, the photoabsorption and photoionization cross sections display a very intense broad feature that is assigned to an ℓ = 4, πg shape resonance. The effect of this shape resonance on the vibrational branching ratios and photoelectron angular distributions is explored. Theoretical calculations of the photoionization cross section and photoelectron angular distributions are in good agreement with the experiments. The results for 2-butyne are compared with those of acetylene, propyne, and 1-butyne, none of which show such significant enhancements near threshold, and the differences are rationalized in terms of the symmetries and orbital angular momenta of the highest occupied orbitals and the corresponding shape resonances. Expectations for larger alkynes and alkynyl radicals are also discussed. A preliminary measurement of the ionization energy of the 2-butyne dimer is also presented. [ABSTRACT FROM AUTHOR]

The ionization potentials of the transient species CH3CH2O, CH3CHOH, and CH2CH2OH (generated by the F+ethanol reactions) are measured by photoionization mass spectrometry: I.P.(CD3CD2O)=10.29±0.08 eV (tentative), I.P.(CH3CHOH)<6.85 eV, and I.P.(CD2CH2OH) ≤8.35±0.06 eV. The latter results in a cation of uncertain structure. These reactions also generate vinyl alcohol (adiabatic I.P.=9.33±0.01 eV) and acetaldehyde. A redetermined appearance potential of CH3CHOH+ from ethanol enables one to infer the proton affinity of acetaldehyde to be ≥183.8±0.2 kcal/mol and an α (C–H) bond energy in ethanol >=91.1 kcal/mol (0 K). The appearance potential of m/e=45 ion from bromoethanol is interpreted as formation of a C2H5O+ isomer having the oxirane structure, with ΔHf00 of ∼173.9 kcal/mol, consistent with earlier alternative measurements. A second increase in the m/e=45 ion yield curve from ethanol is interpreted as formation of this same isomer. This interpretation, and an alternative cycle, lead to a β (C–H) bond energy in ethanol of 98±2 kcal/mol. The implication of the current results to the dynamics of dissociation of ethanol cations is discussed. © 1994 American Institute of Physics. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The photoion yield curves of HOBr+ and Br+ from HOBr are presented. The adiabatic I.P. of HOBr is found to be 10.638±0.003 eV. Autoionizing structure in HOBr+ is tentatively assigned and leads to an adiabatic I.P. of the first excited (A L2 A’) state of ∼11.46 eV. The 0 K threshold of Br+ from HOBr (13.915±0.018 eV) implies D0(HO–Br)≤2.101±0.018 eV≡48.45±0.42 kcal/mol. Together with auxiliary thermochemistry, this value yields ΔHf2980(HOBr) ≥ -13.43 ± 0.42 kcal/mol, in excellent agreement with a recent ab initio value -14.2±1.6 kcal/mol. The resulting proton affinity of BrO is 163.8 kcal/mol. Trends observed in the properties of OX and HOX (X=F, Cl, Br) are utilized to infer new values for ΔH0f(OI) and ΔH0f (HOI). Predictions are made for I.P.(HOI). Proton affinities of OX are seen to increase with heavier X, while the X 2A‘–A 2A’ splitting decreases. [ABSTRACT FROM AUTHOR]

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○f(HNCS)>=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○(NCS) ≤ 72.7 ± 0.8 kcal/mol. Approximate values are obtained for ΔHf0○(HNCS+) and for the proton affinity of NCS. [ABSTRACT FROM AUTHOR]

A photoionization mass spectrometric study of HNCO yields the ionization potential (I.P.) (HNCO)=11.595±0.005 eV and the appearance potential (A.P.) (NCO+/HNCO)≤16.532±0.011 eV at 0 K. A similar study of NCO (generated by F+HNCO) gives I.P. (NCO)=11.759±0.006 eV. These observations lead to D0 (H–NCO)≤110.1±0.3 kcal/mol. Additional analysis enables one to infer 28.4±0.5 kcal/mol ≤ ΔHf00 (NCO)≤32.8±0.7 kcal/mol. The implication of these results for kinetic modeling of the processes for reduction of NOx is discussed. [ABSTRACT FROM AUTHOR]

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)≲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)>=D0(Pn2), where Pn=P, As, Sb, and Bi. [ABSTRACT FROM AUTHOR]

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)>=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. [ABSTRACT FROM AUTHOR]

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○f0 (CH2SH+)=211.5±2.0 kcal/mol (≤213.1±0.2 kcal/mol), this is sufficient to establish ΔH○f0 (CH2S)=28.3±2.0 kcal/mol (≤29.9±0.9 kcal/mol) and ΔH○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. [ABSTRACT FROM AUTHOR]

The products of the reaction of F atoms with CH3SH are studied by photoionization mass spectrometry. Two thresholds, at 7.536±0.003 eV and 9.262±0.005 eV, are observed at mass 47, and identified with the adiabatic ionization potentials of CH2SH and CH3S, respectively. These conclusions are confirmed by additional experiments with CD3SH, where an adiabatic ionization potential of 7.522±0.003 eV is obtained at mass 49 (CD2SH+) and a value of 9.268±0.005 eV is found at mass 50 (CD3S+). From an earlier appearance potential for CH2SH+ (CH3SH) and the present ionization potential of CH2SH, an upper limit for Dd0d (H–CH2SH ) of ≤93.97±0.13 kcal/mol is deduced. By giving weight to the measured proton affinity of CH2S, one obtains D0(H–CH2SH )=92.4±2.0 kcal/mol. The corresponding S–H bond energy in CH3SH derived from a recent kinetics-based value for ΔH0f0(CH3S) is 86.1±0.6 kcal/mol. A discrepancy in the difference of ΔH0f0(CH3S+) and ΔH0f0(CH2SH+) arising from recent theoretical and experimental determinations is resolved in favor of the ab initio values. [ABSTRACT FROM AUTHOR]

The vacuum ultraviolet photoionization mass spectrum of As4 is presented, from the ionization threshold to 600 Å. The apparent adiabatic ionization potential is ≤8.49 eV, but the true value may be significantly lower. Three broad autoionization features are observed, probably comprising members of a Rydberg series converging to the B 2A1 state of As+4. The first fragment, As+3, has an appearance potential (0 K) of 11.23±0.05 eV, from which we extract ΔH0f0(As+3)≤228.7±1.3 kcal/mol. The photoion yield curve of As+2(As2) is obtained under conditions where As2 is dominant in the vapor. The adiabatic ionization potential is 9.69±0.02 eV. Two prominent autoionizing Rydberg series are observed, converging to the A 2Σ+g state of As+2, with an ionization potential of 10.238±0.002 eV. At higher energy, three members of a window resonance series can be seen, converging to the B 2Σ+u state of As+2, with an ionization potential of 15.37 eV. From an upper limit to the partial pressure of As3, equilibrium conditions, and assuming a triangular As3, we deduce ΔH0f0(As3)≥60.0 kcal/mol; other criteria suggest ΔH0f0(As3)[bar_over_tilde:_approx._equal_to]63 kcal/mol. Consequently, the adiabatic ionization potential of As3 is <7.32 eV, and probably ≤7.19 eV. Several implications are drawn, relevant to recent studies of antimony and bismuth clusters. [ABSTRACT FROM AUTHOR]

Gaseous C60 has been studied by photoionization mass spectrometry between the ionization threshold and 40.8 eV. An adiabatic threshold of 7.57±0.01 eV is observed, which may be slightly low due to hot bands. The energy derivative of the photoion yield curve is in rough agreement with the He i photoelectron spectrum on the positions of some peaks, but others are weak or absent. The discrepancy is not attributed to autoionization, but rather to selection rules governing the ejection of low energy electrons into high angular momentum waves. C++60 is observed at higher energies, and becomes ∼0.6 as intense as C+60 at 40.8 eV. The photoion yield curve of C++60, approximately linear well above threshold, appears to exhibit curvature near threshold, thwarting an attempt to make a distinction between two alternative values of the second ionization potential. Fragmentation to form C+58 is only observed at the highest energy, 40.8 eV. The unimolecular decay is modelled by quasiequilibrium theory. In this model, the kinetic shift is of the order of 30 eV, and the minimum energy for dissociation into C+58+C2 seems to be 6.0–6.5 eV. [ABSTRACT FROM AUTHOR]

The vacuum ultraviolet photoionization mass spectrum of CH3OF displays a prominent parent ion peak, whose adiabatic onset is 11.340±0.008 eV, although much lower energy fragmentation processes (CH2O++HF, 8.0 eV; CH2OH++F, 9.3 eV) are possible. These lower energy processes have very low intensity. Two higher energy processes, to CH+3+OF and CH2O++H+F, are observed. Their thresholds are used to determine ΔH0f0 (CH3OF)≥-23.0±0.7 kcal/mol, or D0 (CH3O–F)≤47.4±1.2 kcal/mol. CH2OF+ is a significant fragment, whose appearance energy leads to ΔH0f0 (CH2OF+)≊215.1±0.8 kcal/mol. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The photoion yield curves of N2H+2 , N2H+, and H+2 from N2H2 have been studied by photoionization mass spectrometry. The adiabatic ionization potential of N2H2 determined (9.589 ± 0.007 eV) is in excellent agreement with that obtained by photoelectron spectroscopy (PES). The appearance potential of N2H+ (10.954 ± 0.019 eV at 0 K) is in good agreement with earlier electron impact measurements. The appearance potential of H+2 (<13.526 ±0.03; probably ≤13.403 ±0.036 eV, at 0 K) leads to ΔH0f0 (N2H2) >43.8 ±0.7; probably ≥46.6 ±0.8 kcal/mol. Consequently, proton affinity (PA) (N2) <121.8 ±0.8; probably ≤119.0 ±0.9 kcal/mol, which is in good agreement with results from proton transfer experiments and with most ab initio calculations. The N[larger_closed_square]N ‘‘double bond’’ energy determined from N2H2→2NH is <126.6 ±1.0; probably ≤123.8 ±1.1 kcal/mol. The adiabatic ionization potential of N2H3 is found to be 7.61±0.01 eV. This observation leads to D0 (H2NNH–H)=80.8±0.3 kcal/mol, and D0(HNNH–H)[bar_over_tilde:_approx._equal_to]43.8±1.1 kcal/mol. [ABSTRACT FROM AUTHOR]

The adiabatic I.P. of Si2H6 obtained by a photoionization mass spectrometric study at two temperatures is 9.74±0.02 eV. The first fragment, Si2H+4, initially appears with a shallow slope at ≤10.04±0.02 eV, and with a much steeper slope at ≤10.81±0.02 eV. It is argued that the initial onset corresponds to formation of H2SiSiH+2, while the steeper onset is attributed to formation of H3SiSiH+. The second fragment, Si2H5, has an appearance potential of ≤11.59±0.02 eV (11.41±0.03 is a probable value). Successive decomposition leads to Si2H+2 (from Si2H+4 ) and Si2H+3 (from Si2H+5 ). The photoion yield curve for Si2H+3 also displays shallow and steep onsets. Upper limits for the appearance potentials can be readily extracted, but the true thermochemical onsets are less well defined. Heats of formation (or upper limits) are presented for each of these species. For Si2H+6, Si2H+5, and Si2H+4, the experimental values are in good agreement with recent ab initio calculations. For the daughter species, the experimental values exceed the calculated ones, as expected. [ABSTRACT FROM AUTHOR]

The transient species Si2H5, Si2H4, Si2H3, and Si2H2 have been prepared for the first time, by reactions of F atoms with Si2H6. The species are generated in situ and studied by photoionization mass spectrometry. The adiabatic ionization potentials are (in eV) Si2H5, 7.60±0.05; Si2H4, 8.09±0.03; Si2H3, <7.59; and Si2H2, 8.20+0.01-0.02. In addition, two fragment appearance potential curves were measured, Si2H+3 (Si2H5) and Si2H+2 (Si2H4). By combining these ionization potentials with appearance potentials obtained here and from Si2H6, the following heats of formation (kcal/mol at 0 K) have been inferred: Si2H5, <63.3 (59.2); Si2H4, 67.9±0.9; Si2H3 (∼96); Si2H2, <100.7 (90.2–95.6). The quantities in parentheses are probable values, but less well defined. Structures and structural changes resulting from photoionization are discussed. In particular, Si2H2 and its cation are very likely cyclic (doubly bridged). Heats of formation of cations are also obtained, from which the proton affinities of Si2H2 (199±3 kcal/mol) and Si2H4 (199.9 kcal/mol) are deduced. The structural and energetic differences between corresponding silicon and carbon hydrides are discussed in detail. [ABSTRACT FROM AUTHOR]

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 Å, 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. [ABSTRACT FROM AUTHOR]

Structural features well below the usual Stark field depression of the ionization threshold are observed in the photoionization of N2 in the presence of weak (10–15 V/cm) fields. The energies of the structural features can be simulated by assuming rotational autoionization (ΔJ = -2). They are interpreted as originating from Q (J‘) transitions, forbidden to spontaneously autoionize in the absence of a field. The field relaxes the rigorous autoionization selection rules by l spoilage of the Rydberg electron. The effect appears accentuated for high J, low n* states (J ∼27, 28; n* ∼ 23) and quenches at J∼11, n* ∼ 37. The quenching is attributed to the onset of the Inglis–Teller effect. [ABSTRACT FROM AUTHOR]

Photoionization is observed in HBr (at 300 K) below the adiabatic threshold. The photoion yield curve has structure, and is independent of both pressure and electric field over a large range. The peaks can be simulated rather well by a model which assumes rotational autoionization, with ΔN[bar_over_tilde:_approx._equal_to]-4. This model does not exclude concomitant processes with ΔN=-1,-2,-3. A formal theory is also presented, which describes ΔN=-4 as occurring through successive quadrupole transitions, in second-order perturbation theory. A tentative conclusion is drawn, based on preliminary studies of other molecules, that a type of rotational autoionization can occur in heteronuclear diatomic molecules without an electric field, and in homonuclear diatomic molecules with such a field. The photoionization of DBr has been studied with similar conditions. A corresponding simulation is in good agreement with the observed structure below the adiabatic threshold. In addition, one peak in a triad observed in HBr above threshold, and predicted by an MQDT calculation to be absent in DBr, is still observed. [ABSTRACT FROM AUTHOR]

The adiabatic ionization potential of GeH+4 (GeH4) is measured by photoionization mass spectrometry to be ≤10.53 eV and perhaps as low as 10.44 eV. This is about 0.8 eV (∼9 vibrational quanta) lower than the value reported by photoelectron spectroscopy. This result, analogous to that found for SiH+4 (SiH4), implies a marked Jahn–Teller distortion of GeH+4. The appearance potentials of GeH+2 and GeH+3 from GeH4 are ≤10.772±0.009 eV and <11.657±0.01 eV, respectively. The reaction of F atoms with GeH4 generates GeH3, GeH2 (weakly), and some atomic germanium. The adiabatic ionization potential of GeH3 is ≤7.948±0.005 eV; that of GeH2 is ≤9.25 eV. Together with auxiliary information, limits (more probable values) of the incremental bond energies, in kcal/mol, are found to be D0 (H3Ge–H) <85.5 (82±2); D0 (H2Ge–H) >56.4 (59); D0 (HGe–H) <68.9 (66); and D0 (Ge–H) >53.7 (63). These specific bond energies, when appropriately normalized, display the same pattern as the SiHn (but not the CHn) bond energies and provide a basis for estimating the corresponding SnHn bond energies. [ABSTRACT FROM AUTHOR]

A photoionization mass spectrometric study has been performed on the products of the F+HCOOH, F+DCOOH, and F+HCOOD reactions. Hydrogen/deuterium abstraction on the carbon site yields the COOH/COOD radical which can be photoionized and detected. Abstraction on the oxygen site also occurs, but does not yield a detectable isomeric HCOO/DCOO product. Instead, CO2 is readily observed, implying that HCOO/DCOO is unstable to decomposition under the conditions of this experiment. The detection of COOH is believed to be the first experimental evidence for the stability of this species in the gas phase. An adiabatic ionization potential of 8.486±0.012 eV is obtained. Combined with the recently obtained ΔHf00 (COOH+)=143.2±0.5 kcal/mol, this ionization potential leads to ΔHf00 (COOH)=-52.5±0.6 kcal/mol. Hence, COOH is stable with respect to the lowest energy dissociation products (H+CO2) by 10.2±0.6 kcal/mol. [ABSTRACT FROM AUTHOR]

The dissociative ionization of HCOOH to form COOH+ +H+e has been reinvestigated. Experiments with DCOOH and HCOOD demonstrate that rearrangement competes with direct bond cleavage in this dissociation, even near threshold. Extrapolation of the photoion yield curve of COOH+ to the background level is ambiguous. A photoelectron–photoion coincidence experiment was thereupon performed, to obtain a breakdown diagram. From the 0 K cross over energy of 12.30±0.02 eV, we infer ΔHf00 (COOH+)=143.2±0.5 kcal/mol, and proton affinity (PA) (CO2)=129.2±0.5 kcal/mol. Some possible mechanisms for the rearrangement process are explored, but the calculated barriers are too high to explain the observation. [ABSTRACT FROM AUTHOR]

The ethyl radical has been produced by the F+C2H6 reaction, and studied by photoionization mass spectrometry. The adiabatic ionization potential (IP) is found to be 8.117±0.008 eV. The radical and cation have been studied by the G1 level of molecular orbital theory. The calculated adiabatic ionization potential is 8.06 eV. On the basis of both experiment and theory, it is concluded that the cation in its ground state has a bridged structure. The adiabatic value resolves a previous inconsistency involving ΔH○f(C2H5), ΔH○f(C2H+5) and IP (C2H5). Broad autoionizing structures are observed at higher energy. These features can be rationalized as Rydberg states converging to the first excited state 3A‘ calculated to be at 12.05 eV. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The reactions of H/D with C2H6 and C3H8 have been studied with both shock-tube experiments and ab initio transition-state theory calculations. Rate constants for the reactions of D with C2H6 and C3H8 have been measured in reflected shock wave experiments over the temperature range, 1128-1299 K, at pressures 0.3-1 atm. D atoms are detected using atomic resonance absorption spectrometry. The measured D-atom profiles are sensitive to only the thermal dissociation of the D-atom source molecule, C2D5I, and to the title reactions. Since the dissociation has been previously studied in this laboratory, modeling the temporal evolution of the D-atom profiles allows determinations of the rate constants for the title reactions. Over the T range, 1128-1228 K, rate constants from the present experiments for D + C2H6 can be represented by the Arrhenius expression [ABSTRACT FROM AUTHOR]