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  • 1
    Electronic Resource
    Electronic Resource
    Spectroscopic analysis of an unusual Ca⋅Xe[3Σ−]←Ca(4s4pπ 3P0)⋅Xe[3Π0−] transition (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 6434-6438 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: From the partially resolved rotational structure of six vibrational bands at high resolution, a vibrational progression in the 22 400–22 900 cm−1 region has been assigned to a CaXe[3Σ−]←Ca(4s4pπ 3P0)⋅Xe[3Π0−] transition. It is suggested that the CaXe[3Σ−] state observed is a "mixed" state, having both Ca(4pπ4pπ 3PJ)⋅Xe[3Σ−] and Ca(3dπ4pπ 3DJ)⋅Xe[3Σ−] character due to an adiabatic avoided crossing between the two diabatic states. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480020
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  • 2
    Electronic Resource
    Electronic Resource
    Spectroscopic characterization of the unusually strongly bound, doubly excited van der Waals state, Mg(3pπ3pπ 3PJ)⋅Kr[3Σ−] (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 7777-7783 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The unusual doubly excited van der Waal's state, Mg(3pπ3pπ 3PJ)⋅Kr[3Σ−], has been characterized using a laser-vaporization, supersonic-jet source and R2PI (Resonance Two-Photon Ionization) spectroscopy. This state is very strongly bound (De=3966 cm−1) and has a short bond length (Re=2.45 Å) compared to its singly excited analogue, Mg(3s3pπ 3PJ)⋅Kr[3Π0−], for which De=267 cm−1 and Re=3.48 Å. In fact, this state is even more than twice as strongly bound as the ground-state Mg(3s)+⋅Kr ion, where De=1949 cm−1 and Re(approximate)2.8 Å. Possible reasons for the strong van der Waal's bonding are discussed, and it is concluded that the lack of σ-σ repulsion because there is no Mg(3sσ) valence electron must be a major factor; the similar ionic van der Waal's state Mg+(3pπ)⋅Kr[2Π], which would be obtained by removing one of the Mg(3pπ) electrons, is even more strongly bound, with De(approximate)7200 cm−1 [J. S. Pilgrim, C. S. Yeh, K. R. Berry, and M. A. Duncan, J. Chem. Phys. 100, 7945 (1994)]. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477423
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  • 3
    Electronic Resource
    Electronic Resource
    Spectroscopic characterization of excited Ca(4s4dδ 3DJ)RG(3Δ1,2) states (RG=Ar, Kr, Xe): No "heavy-atom" mixing of RG(ndδ) character into the wave functions (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 981-987 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The excited Ca(4s4dδ 3DJ)RG[3Δ1,2] states (RG=Ar, Kr, Xe) have been characterized spectroscopically by R2PI (resonance-enhanced two-photon ionization) spectroscopy. The main vibrational progressions, assigned to Ca(4s4dδ 3D1)RG[3Δ1]←Ca(4s4pπ 3P0)⋅RG[3Π0〈sup ARRANGE="STAGGER"〉−] transitions, have weak subbands 3.7±0.5 cm−1 to the blue which have been assigned to analogous transitions to the 3Δ2 upper states. For CaAr and CaKr, rotational analysis has confirmed this assignment. The 3Δ2/3Δ1 splitting is within experimental error the value expected if the molecular spin-orbit coupling constant is derived entirely from the Ca(4s4d 3DJ) atomic contribution. This indicates that there is no "heavy-atom" mixing of RG(ndδ) character into the wave functions of the CaRG(3Δ) states. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479380
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  • 4
    Electronic Resource
    Electronic Resource
    An ab initio study of the ground states and some excited states of BeRG, Be+RG, and Be+2RG van der Waals complexes (RG=He, Ne) (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 9197-9202 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: By ab initio methods, we have characterized the potential curves of the unusual, doubly excited valence van der Waals states, Be(2pπ+12pπ−1 3PJ)⋅RG[3Σ−], where RG=He, Ne. Similar to the Mg(3pπ+13pπ−1 3PJ)⋅RG[3Σ−] states (RG=He, Ne, Ar, Kr) which were characterized experimentally and theoretically earlier, these Be(2pπ2pπ 3PJ)⋅RG[3Σ−] states are much more strongly bound than their singly excited Be(2s2pπ 3PJ)⋅RG[3Π] analogs, and even much more strongly bound than the analogous Be+(2s 2S)⋅RG[2Σ+] ground-state ions. This is attributed to the lack of a large Be(2s) electron cloud with density along the internuclear axis, so that quadrupole/induced-dipole and dispersion attraction forces can proceed to much smaller internuclear distances before repulsion sets in. The BeHe[3Σ−] state is also almost five times more bound than the BeNe[3Σ−] state, despite the fact that the polarizability of the He atom is only one-half that of the Ne atom. This is again attributed to minimization of repulsive forces, since strong Be(2pπ)/RG(npπ) exchange repulsion is completely absent when RG=He. The fact that the bond strengths of the Be(2pπ2pπ)⋅He[3Σ−] and Be+(2pπ)⋅He[2Π] states are quite similar, and only about 20% less than the bond strength of the free Be++⋅He[1Σ+] ion, is consistent with this interpretation. All of the strongly bound Be⋅RG neutral and ionic states calculated here have bond strengths greater than, and bond lengths smaller than, their Mg⋅RG analogs. This is because the Be electron clouds are all smaller than their Mg analogs, so that, again, all attractive forces can proceed to smaller distances before repulsion sets in. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479833
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  • 5
    Electronic Resource
    Electronic Resource
    Spectroscopic characterization of the weakly bound Ca(4s4dσ 3D3)⋅Ar[3Σ+] state: Evidence for a substantial maximum in the potential curve at long range (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 2484-2489 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The weakly bound Ca(4s4dσ 3D3)⋅Ar[3Σ+] state has been characterized by means of R2PI (Resonant Two-Photon Ionization) spectroscopy, using transitions from the Ca(4s4pπ 3P0)⋅Ar[3Π0−] metastable state prepared in a laser-vaporization/supersonic jet source. Because several of the vibrational levels are above the dissociation limit [to Ca(4s4d 3D3)+Ar(1S0)], it is concluded that there must be a substantial maximum in the Ca(4s4dσ 3D3)⋅Ar[3Σ+] potential curve (〉200 cm−1) at large R (〉4.0 Å). This is discussed, and shown to be consistent with our earlier ideas of "penetration" of outerlobes of electron density of metal atom excited states by RG (rare-gas) atoms. Perturbations observed, due to possible potential curve crossings with states of different electronic symmetry, are also discussed. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479526
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  • 6
    Electronic Resource
    Electronic Resource
    Potential curves for several electronic states of the MgHe, Mg+He, and Mg+2He van der Waals complexes (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 4999-5003 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have estimated the potential curves of the Mg(3s3pπ)⋅He[3Π], Mg(3pπ3pπ)⋅He[3Σ−], Mg+(3s)⋅He[2Σ+], Mg+(3pπ)⋅He[2Π], and Mg+2(2p6)⋅He[1Σ+] van der Waals states by means of ab initio calculations. Similar to the analogous doubly excited states of MgNe, MgAr, and MgKr, the Mg(3pπ3pπ)⋅He[3Σ−] state is found to be unusually strongly bound, De=2386 cm−1, a bond strength which is an astounding 165 times that of the singly excited Mg(3s3pπ)⋅He[3Π] state and 35 times that of the Mg+(3s)⋅He ion. The strong bonding is attributed primarily to the lack of a Mg(3s) electron, so that all the attractive forces can extend to smaller internuclear distances because there is no Mg(3sσ)/He(1sσ) repulsion. In fact, the Mg(3pπ3pπ)⋅He[3Σ−], Mg+(3pπ)⋅He[2Π], and Mg+2(2p6)⋅He[1Σ+] states have quite similar bond energies and bond lengths, indicating that for RG=He, the primary attractive force in all these states is the ion/induced-dipole interaction of the "Mg+2/He" core. This is consistent with the fact that the bond energy of the Mg(3pπ3pπ)⋅He[3Σ−] state is more than four times greater than that of the Mg(3pπ3pπ)⋅Ne[3Σ−] state, where there is substantial Mg(3pπ)/Ne(2pπ) repulsion not present in the Mg(3pπ3pπ)⋅He[3Σ−] state. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479737
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  • 7
    Electronic Resource
    Electronic Resource
    Potential curves for the ground states and some excited states of MgNe, Mg+Ne, and Mg+2Ne van der Waals complexes (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 8443-8447 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have estimated the potential curves of the Mg(3s2)⋅Ne(1Σ+), Mg(3s3p)⋅Ne(3Π,3Σ+), Mg(3p2)⋅Ne(3Σ−), Mg+(3s)⋅Ne(2Σ+), Mg+(3p)⋅Ne(2Π), and Mg+2(2p6)⋅Ne(1Σ+) van der Waals states by means of ab initio calculations. Similar to the analogous doubly-excited states of MgAr and MgKr, the Mg(3pπ3pπ)⋅Ne(3Σ−) state is found to be unusually strongly bound, De=548 cm−1, a bond strength which is more than 20 times that of the singly-excited Mg(3s3pπ)⋅Ne(3Π) state and even more than three times that of the Mg+(3s)⋅Ne ion. The strong bonding is attributed primarily to the lack of a Mg(3s) electron, so that all the attractive van der Waals forces can extend to smaller internuclear distances because there is no Mg(3sσ)/Ne(2pσ) exchange repulsion. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478805
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  • 8
    Electronic Resource
    Electronic Resource
    Resonant two-color photoionization threshold measurements of the Zn+(4s)⋅Ar bond strength: Model-potential analysis of M+(ns)⋅Ar interactions (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 6298-6305 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The bond energy of the Zn(4s)+⋅Ar ground-state ion has been determined to be De=2085±100 cm−1 by measuring the threshold for two-color resonant photoionization of a ZnAr metastable state. This bond energy is larger (and the estimated bond length is smaller) than the values for other similar M(ns)+⋅Ar states, where M=Mg, Ca, V, Co, Ba, Cd, and Hg, consistent with our earlier postulate that the Zn(4s)+ "core" is smaller than the other M(ns)+ cores in the analogous electronically excited MAr van der Waals complexes for M=Mg, Ca, Zn, Cd, and Hg. We analyze and compare the M+(ns)⋅Ar potential curves using a model potential consisting of calculated 1/R4 (dipole induction) and 1/R6 (quadrupole induction plus dispersion) attractive terms, and an empirically derived Ae−bR repulsion term. The repulsion term for Zn+Ar is consistent with our postulate, in that at smaller R it is the least repulsive of the M+(ns)⋅Ar repulsive potentials when M=Zn, Hg, V, Co, Cd, Mg, Ca, and Ba. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478534
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  • 9
    Electronic Resource
    Electronic Resource
    Spectroscopic characterization of the metastable 3pπ 3Π0+,0− valence states and the 4s3Σ+ Rydberg states of the MgKr and MgXe van der Waals molecules (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 10492-10505 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The first metastable valence excited states and the first Rydberg states of the MgKr and MgXe molecules have been characterized by resonance two-photon photoionization (R2PI) spectroscopy. The Mg(3s3p 3PJ)⋅RG(3Π0+,0−) metastable states, produced by expanding the products of a laser-ablated magnesium rod in Kr/Ar or Xe/Ar gas mixtures into a supersonic expansion, were excited by a dye laser pulse to several vibrational levels of the Mg(3s4s 3S1)⋅RG(3Σ+) Rydberg states, with detection by ionization with a second dye laser pulse. Spectroscopic constants, bond energies, and bond lengths are reported for both states of MgKr and MgXe. The 3Σ+ Rydberg states are much more strongly bound than the lower 3Π0− valence states, and in fact are essentially as strongly bound as the ground states of the analogous MgRG+ ions, characterized previously in the same apparatus. This clearly indicates that the RG atoms can readily penetrate the diffuse Mg(4s) Rydberg electron cloud. The interesting and unusual spin–orbit and "spin–spin" effects observed are attributed to mixing of some RG character into wave functions of predominantly Mg* excited state character. Bonding and spin–orbit interactions in the MgAr, MgKr, and MgXe first triplet metastable and Rydberg states are discussed. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474213
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  • 10
    Electronic Resource
    Electronic Resource
    Reactions of Zn(4s4p 3P1) and Cd(5s5p 3P1) with SiH4 (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 9401-9407 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The first nsnp 3P1 excited states of Cd and Zn atoms are shown to readily activate Si–H bonds in SiH4. The nascent quantum state distributions of the CdH(v;N) and ZnH(v;N) products in the reactions of Cd(3P1) and Zn(3P1) with SiH4 have been determined using the laser pump–probe technique. The results are discussed within the context of our current knowledge about the chemical interactions of valence M(nsnp 3P) excited states with Si–H, H–H, and C–H bonds, where M=Mg, Zn, Cd, and Hg. It is proposed that the high reactivity of M(nsnp 3P1) states with H–H and Si–H bonds compared to C–H bonds is simply due to the lack of steric hindrance in the localized, side-on, M(npπ)–XH(σ*) donor–acceptor molecular orbital interactions, since the Si–H bond-length in SiH4 is ∼1.5 A(ring) compared to C–H bond lengths of ∼1.1 A(ring). © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471685
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