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  • American Institute of Physics (AIP)  (10)
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  • 1
    Electronic Resource
    Electronic Resource
    Mass analyzed threshold ionization of the 35Cl and 37Cl isotopomers of p-chloroaniline (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 4109-4115 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: One-color, two-color resonant two-photon ionization (R2PI), and mass analyzed threshold ionization (MATI) spectroscopic methods have been used to study the electronic transition and the threshold ionization of the 35Cl and 37Cl isotopomers of p-chloroaniline. The band origins of the S1←S0 electronic transitions of both species are found to be 32 573±1 cm−1. The ionization energies (IEs) of both isotopomers of p-chloroaniline are determined to be 62 409±7 cm−1 by the two-color R2PI spectroscopy and 62 410±4 cm−1 by the MATI spectroscopy. Analyses on the spectral features show that most of the active modes are related to the in-plane ring vibrations in the S1 state and cationic ground state. Isotope effect on the ring deformation vibrations 1, 6a, and 12 gives rise to a frequency shift of 1–3 cm−1 in the S1 state and 3–9 cm−1 in the ion state. The experimental results are well supported by the computed ones on the basis of ab initio and density functional theory calculations. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1288147
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  • 2
    Electronic Resource
    Electronic Resource
    Determination of laser beam waist using photoionization time-of-flight mass spectrometer (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 2776-2780 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A method for the determination of a focused laser beam waist via photoionization and retarding potential analysis is discussed. The focused laser beam was employed to photoionize gas phase clusters generated from a supersonic cluster source. It intersects the cluster beam at right angle in the first stage of the time-of-flight (TOF) acceleration lens assembly. With a simple modification on a laser-based TOF mass spectrometer, retarding fields were applied right in front of the microchannel plate ion detector to map out the kinetic energy distribution of the cluster ions. The size of the laser beam along the molecular beam axis in the ionization region can then be directly related to this energy distribution. In addition, this method manifests a sensitive probe (within 10 μm) to the laser beam position.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144615
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  • 3
    Electronic Resource
    Electronic Resource
    Photoionization study of HgAr (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 648-652 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Photoionization efficiency data for HgAr+ have been obtained in the region of 680–1240 A(ring). The ionization energy of HgAr was determined to be 10.217±0.012 eV. This value allows the calculation of the dissociation energy of HgAr+ to be 0.228±0.017 eV. The relative probabilities for the formation of HgAr+ via the reactions Ar* ⋅ Hg or Hg* ⋅ Ar→ HgAr+ +e− with Ar* and Hg* prepared in high Rydberg states in the energy range of 10.22–15.79 eV were estimated. Although the radii for the 3d and 5s Rydberg ortitals of Ar have similar values, the probabilities for the formation of HgAr+ from Hg ⋅ Ar* with Ar* in the 5s[3/2]01 and 5s'[1/2]01 Rydberg states are substantially greater than those when the Ar* excited atoms are in the 3d[1/2]01, 3s[3/2]01, and 3d'[3/2]01 Rydberg levels. The ratio for the cross sections for the formation of HgAr+ from Hg ⋅ Ar* with Ar* formed in the 3d[1/2]01 and 4d[1/2]01 states, as well as that with Ar* prepared in the 5d[1/2]01 and 6d[1/2]01 states, were found to be consistent with the predictions of the previous impact parameter calculations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.448539
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  • 4
    Electronic Resource
    Electronic Resource
    A study of the unimolecular decompositions of the (C3H6)+2 and (c-C3H6)+2 complexes (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 2803-2812 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The major product channels identified in the unimolecular decompositions of C3H+6⋅C3H6 and c-C3H+6⋅c-C3H6 in the total energy [neutral (C3H6)2 or (c-C3H6)2 heat of formation plus excitation energy] range of ∼230–450 kcal/mol are C3H+7+C3H5, C4H+7+C2H5, C4H+8+C2H4, and C5H+9+CH3. The measured appearance energy for C4H+7(9.54±0.04 eV) from (C3H6)2 is equal to the thermochemical threshold for the formation of C4H+7+C2H5 from (C3H6)2, indicating that the exit potential energy barrier for the ion–molecule reaction C3H+6+C3H6→C4H+7+C2H5 is negligible. There is evidence that the formations of C4H+7+C2H4+H from (C3H6)+2 and (c-C3H6)+2 also proceed with high probabilities when they are energetically allowed. The variations of the relative abundances for C4H+7,C4H+8, and C5H+9 from (C3H6)+2 and (c-C3H6)+2 as a function of ionizing photon energy are in qualitative agreement, suggesting that (C3H6)+2 and (c-C3H6)+2 rearrange to similar C6H+12 isomers prior to fragmentation. The fact that C6H+11 is found to be a primary ion from the unimolecular decomposition of (c-C3H6)+2 but not (C3H6)+2 supports the conclusion that the distribution of C6H+12 collision complexes involved in the C3H+6+C3H6 reactions is different from that in the cyclopropane ion–molecule reactions. Using the ionization energies (IE) of (C3H6)2(9.33±0.04 eV) and (c-C3H6)2(9.61±0.04 eV) determined in this study, the calculation of the bond dissociation energies for C3H+6⋅C3H6 and c-C3H+6⋅c-C3H6 gives 0.43 and 0.14 eV, respectively. The measured IE of C3H6 is 9.738±0.003 eV and that of c-C3H6 is 9.721±0.011 eV.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449229
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  • 5
    Electronic Resource
    Electronic Resource
    A study of the unimolecular decomposition of the (C2H4)+3 complex (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 2813-2817 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The energetics and dissociation dynamics of the (C2H4)+3 complexes have been studied by photoionization of neutral van der Waals ethylene trimers. The major product channels identified in the unimolecular decomposition of (C2H4)+3 in the total energy [neutral (C2H4)3 heat of formation plus excitation energy] range of ∼260–336 kcal/mol are C3H+6 +C3H6, C3H+7 +C3H5, C4H+7 +C2H5 (or C2H4+H), C4H+8 [or (C2H4)+2 ]+C2H4, C5H+9 +CH3, and C6H+11+H. The fact that these product channels are similar to those observed in the unimolecular decompositions of (C3H6)+2 and (c-C3H6)+2 is consistent with the interpretation that the (C2H4)+3 , (C3H6)+2, and (c-C3H6)+2 loose complexes rearrange to similar stable C6H+12 ions prior to fragmenting. The ionization energies (IE) of (C2H3)3 and (C2H4)4 are determined to be 9.465±0.036 (1310±5 A(ring)) and 9.287±0.034 eV (1335±5 A(ring)), respectively. Using the known IE's of (C2H4)n, n=2, 3, and 4, and the estimated binding energies of (C2H4)2 ⋅ C2H4 and (C2H4)3 ⋅ C2H4, the bond dissociation energies for (C2H4)+2 ⋅ C2H4 and (C2H4)+3 ⋅ C2H4 are deduced to be 9.2±1 and 4.6±1 kcal/mol, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449230
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  • 6
    Electronic Resource
    Electronic Resource
    Spectroscopy of phenylacetylene bound to clusters of ammonia and the surface cluster analogy (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 11-18 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The results of a systematic study of the spectra shifts of the S1–S0 transition in phenylacetylene (PA) [1B2(1Lb)←1A1(1A)] due to solvation by NH3 are reported based on two-photon REMPI. A unique aspect of the present work is comparison of the red shifts for clusters produced by coexpansion techiques with those where PA is attached to performed ammonia clusters. In both experiments the 1–1 complex is red shifted by 80 cm−1. In the case of the coexpansion experiments the red shift is about 50 cm−1 for PA(NH3)n, n=2–7. By contrast, the clusters produced by attachment display a much different and gradually increasing red shift which saturates at 150 cm−1 for n=13 and beyond. Structural differences for clusters produced by the two different techniques are believed to be responsible.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456517
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  • 7
    Electronic Resource
    Electronic Resource
    Kinetic energy release measurements of ammonia cluster ions during metastable decomposition and determination of cluster ion binding energies (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 332-339 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The dissociation dynamics of protonated ammonia clusters is investigated following their production from neutrals using multiphoton ionization. A very useful method of measuring the kinetic energy release arising from evaporative unimolecular dissociation is established; it employs a time-of-flight/reflectron to separate daughters and parents and enables the energy release to be determined from the peak shapes. The method is found to lead to values of high precision. Using a modified statistical theory analysis suggested by Engelking, it is shown that binding energies for large cluster ions can be readily determined. The results compare very well with those derived by other methods, ones which generally have much more severe size limitations. In the case of (NH3)n H+, the observed drop in binding energy from n=5 to 6 is consistent with the particularly stable protonated pentamer structure. Heretofore, unavailable results are available from n=7 to 17, with hints of slightly more stable cluster ions at n=12 and 14, than for neighboring size clusters. The unimolecular dissociation is found to proceed by a statistical evaporative mechanism, with average kinetic energy releases showing a general decrease with size beyond n=5; small local maxima are found in regions of particularly stable structures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458434
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  • 8
    Electronic Resource
    Electronic Resource
    Dissociation dynamics: Measurements of decay fractions of metastable ammonia cluster ions (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 2506-2512 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The decay fractions of metastable ammonia cluster ions which undergo unimolecular (evaporative) dissociation in a time window of 1–40 μs were measured by using a reflection time-of-flight mass spectrometer. Corrections concerning instrumental artifacts and ion trajectory of parents and daughters are made to imporve the precision of the measurements. The data are used to derive the Gspann parameter and heat capacity of clusters as described in evaporative ensemble model of metastable dissociation. Using the dissociation fractions measured in the present studies, in conjunction with kinetic energy release values previously measured in our laboratory, we apply Klots' evaporative ensemble model to obtain binding energies of ammonia cluster ions (NH3)nH+, 4≤n≤17. The deduced binding energy values are found to be in very good agreement with both thermochemical data and Engelking's modified statistical theory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459033
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  • 9
    Electronic Resource
    Electronic Resource
    Intracluster reactions in phenylacetylene ammonia clusters initiated through resonant enhanced ionization (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 19-24 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Protonated ammonia clusters of specific size are observed to form following the resonant enhanced ionization of phenylacetylene–ammonia clusters PA⋅(NH3)n in the 000 region of the S1–S0 transition of the (unclustered) PA. The resonance enhanced absorption of two photons, ≈8.8 eV total energy, are found to cause intracluster reactions for n≥5. The findings imply that the adiabatic ionization potential of (NH3)4 is greater than 8.8 eV, while that of (NH3)5 is (slightly) less.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456521
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  • 10
    Electronic Resource
    Electronic Resource
    A 193 nm laser photofragmentation time-of-flight mass spectrometric study of CS2 and CS2 clusters (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 1658-1669 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A crossed laser and molecular beam photofragmentation apparatus is described. The apparatus is equipped with a rotatable molecular beam source and a translationally movable ultrahigh vacuum mass spectrometer for time-of-flight (TOF) measurements. Using this apparatus we have measured the TOF spectra of S and CS resulting from the photofragmentation processes, CS2+hν(193 nm)→CS(X,v)+S(1D or 3P). The translational energy distributions of photofragments derived from the S and CS TOF spectra are in good agreement. This observation, together with the finding that the TOF spectra of S and CS are independent of laser power in the 25–150 mJ range, shows that the further absorption of a laser photon by CS to form C(3P)+S(3P) within the laser pulse is insignificant. The TOF spectra of S obtained at electron ionization energies of 20 and 50 eV are indiscernible, indicating that the contribution to the TOF spectrum of S from dissociative ionization of CS is negligible at electron impact energies ≤50 eV. The thermochemical thresholds for the S(1D) and S(3P) channels are determined to be 18.7 and 45.0±0.4 kcal/mol, respectively, consistent with literature values. Structures found in the translational energy distribution can be correlated with vibrational structures of CS(X,v=0–5) associated with the S(1D) channel. The translational energy distribution supports the previous observation that the vibrational state distribution of CS(X,v) is peaked at v=3. The TOF experiment is also consistent with the S(3P)/S(1D) ratio of 2.8±0.3 determined in a recent vacuum ultraviolet laser induced fluorescence measurement on the S photofragment. Photofragments from CS2 clusters are observed at small laboratory angles with respect to the CS2 beam direction and are found to have velocity distributions peaked at the CS2 cluster beam velocity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454144
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