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  • 11
    Electronic Resource
    Electronic Resource
    Optothermal-detected microwave-sideband CO2-laser spectroscopy of Ar–NH3 (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 7061-7067 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A microwave-sideband CO2-laser optothermal spectrometer with a resolution better than 1 MHz has been used to record the infrared spectrum of Ar–NH3 in the vicinity of the aR(0,0) line of the ν2 vibration of free NH3. A Π←∑ type band is observed, giving a positive l-type doubling constant q, of 90.9 MHz for the upper state. The positive q indicates that the j=1, k=0, ∑ state is above the j=1, k=0, Π state in the v2=1 excited state, where j and k specify the correlation of the internal-rotor state of the Ar–NH3 complex to the NH3 monomer rotational state j,k. The ν2 vibrationally excited complex is found to predissociate in less than the 0.9 ms transit time between the bolometer detector and laser-excitation region. A lower limit to the upper-state lifetime can be obtained from the observed linewidths, which range from 1.5 to 3 MHz (FWHM). The present results agree with and extend the previous free-jet diode-laser absorption measurements on this band.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460239
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  • 12
    Electronic Resource
    Electronic Resource
    Infrared and microwave spectra of OCO–HF and SCO–HF (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 1330-1336 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The H–F stretching bands of the OCO–HF and SCO–HF complexes have been studied by optothermal (bolometer-detected) molecular-beam spectroscopy. Both species exhibit spectra of a quasilinear molecule red shifted from free HF by 52.1 and 57.5 cm−1, respectively. The principal band in both molecules is accompanied by a slightly red-shifted doublet-type subsidiary band that can be interpreted as a hot band of a low frequency bending vibration or a K=1 subband of a bent molecule. Accurate doublet splittings in the ground H–F vibrational state have been measured by pulsed-nozzle Fourier-transform microwave spectroscopy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456074
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  • 13
    Electronic Resource
    Electronic Resource
    Microwave electric-resonance optothermal spectroscopy of (H2O)2 (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 6077-6085 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The microwave spectrum of (H2O)2 has been measured between 14 and 110 GHz using a newly developed electric-resonance optothermal spectrometer (EROS) described here. The reported measurements extend previous results on the a-type Ka=0–0 and 1–1 bands for the A±2 , B±2 , and E± rotational-tunneling states and include the first observations of the c-type Ka =1–0 band for the A±2 and B±2 states and the a-type Ka =0–0 band for the A±1 states. For the A±1 states an interconversion tunneling splitting of 22.6 GHz is obtained, compared to the 19.5 GHz value found previously for the Ka =0 A±2 and B±2 states.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456373
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  • 14
    Electronic Resource
    Electronic Resource
    P-type doubling in the infrared spectrum of NO–HF (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 2992-3004 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The HF stretching band of the NO–HF open-shell complex has been recorded using a molecular-beam optothermal spectrometer. The spectrum exhibits P-type doubling indicative of an unpaired electron spin coupled to the rotational angular momentum of a bent complex with substantially quenched electron orbital angular momentum. From B¯‘=0.111 320(17) cm−1, and an off-axis angle for the NO of 30°, the zero-point center-of-mass separation is estimated to be 3.4396(3) A(ring). The HF frequency shift of 84 cm−1 indicates that the complex is hydrogen bonded, and the spectral intensities imply that the HF axis is aligned closely to the center-of-mass axis and the NO is off axis by 30±15°. The Renner–Teller-like orbital quenching parameter is somewhat larger than the spin–orbit constant in the free NO molecule and increases substantially upon vibrational excitation. The transitions in this band exhibit vibrational predissociation broadening of 200±40 MHz (FWHM), similar to that observed for a number of closed-shell hydrogen-bonded HF complexes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458886
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  • 15
    Electronic Resource
    Electronic Resource
    Pulsed-nozzle Fourier-transform microwave spectroscopy of laser-vaporized metal oxides: Rotational spectra and electric dipole moments of YO, LaO, ZrO, and HfO (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 4724-4733 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The rotational spectra of YO, LaO, ZrO, and HfO have been measured using a Fourier-transform microwave spectrometer in combination with a laser-ablation source. Here, a Q-switched Nd:YAG laser (532 nm) was used to vaporize the metal oxides from a target source rod located in the throat of a pulsed-molecular-beam valve. A description of the instrument is given. The electric dipole moments of the four species have been measured and compared to ab initio results, where available. The experimental values are μYO =4.524(7), μLaO =3.207(11), μZrO =2.551(11), and μHfO =3.431(5) D. Of special note are the extremely large nuclear quadrupole coupling constants, eQq, determined for the 177HfO and 179HfO isotopic species, with values of −5952.649(35) MHz and −6726.981(39) MHz, respectively. This is the first determination of nuclear quadrupole coupling constants for a molecule containing the Hf atom.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457690
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  • 16
    Electronic Resource
    Electronic Resource
    Fragmentation of NH3 dimers by electron impact ionization (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 3028-3031 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The fragmentation of ammonia dimers by electron impact ionization is investigated by preselecting the neutral species using scattering and spectroscopic methods. In the first experiment, the measured angular and velocity dependence of the ammonia cluster scattered from a helium beam is used to separate the dimer from the other contributions. In the second experiment, the rotationally resolved spectrum obtained by microwave electric resonance technique is used to label the dimer. The ratio of the ion intensities m=18 (NH+4) to m=17 (NH+3) amu is 1.3 and 1.8, respectively. In the case of scattering, the result is independent of the initial state distribution of the dimer. The remaining difference is attributed to the different ion sources. This remarkable result is explained in terms of simple models based on the structural change from the neutral to the ionized configuration and the fragmentation pattern of the monomer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453945
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  • 17
    Electronic Resource
    Electronic Resource
    Microwave and submillimeter spectroscopy of Ar–NH3 states correlating with Ar+NH3 (j=1,||k||=1) (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 793-803 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Microwave and submillimeter transitions for Ar–NH3 have been observed and assigned for the ∑ and Π states correlating asymptotically with Ar+NH3 (j=1,||k||=1). The ∑ states are found to lie below the Π states and are separated by approximately the inversion splitting of free NH3. For the Π states the NH3 inversion tunneling is nearly quenched, being only weakly allowed through Coriolis interactions with the nearby ∑ states. The observed microwave and submillimeter spectra also allow the determination of 14N quadrupole coupling constants and relative submillimeter absorption intensities. All the above results are interpreted using a model internal–rotation inversion Hamiltonian, leading to detailed information about the anisotropy of the intermolecular potential.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461086
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  • 18
    Electronic Resource
    Electronic Resource
    Infrared and microwave study of angular–radial coupling effects in Ar–HCN (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 3319-3326 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Microwave and infrared spectra of Ar–HCN have been obtained using an electric-resonance optothermal spectrometer. The microwave measurements extend to higher J the previous results of Leopold et al. and Klots et al., allowing the determination of higher-order centrifugal distortion constants for this quasilinear, highly nonrigid complex. A Padé approximant fit to the microwave data indicates a significant rotation-induced asymptotic increase in the zero-point center-of-mass separation between the Ar and the HCN, above that expected from pure radial distortion. This results from the large coupling between the angular and radial degrees in the intermolecular potential forcing the centrifugal alignment of the HCN. Infrared spectra are reported for the C–H streching fundamental ν1 and the combination band ν1+ν15, where ν5 is the van der Waals bending vibration. The band-origin difference between these two bands gives ν5=7.8 cm−1, in rough agreement with the 10 cm−1 harmonic value predicted from the microwave-determined nuclear quadrupole coupling constant. The complexation-induced red shift of the C–H stretching vibration is 2.69 cm−1 and the vibrational predissociation linewidths Γ are 〈10 MHz (FWHM). The vibrationally excited complex predissociates before striking the bolometer detector, implying that the predissociation lifetime τ〈1 ms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456907
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  • 19
    Electronic Resource
    Electronic Resource
    Microwave and infrared electric-resonance optothermal spectroscopy of HF–HCl and HCl–HF (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 637-645 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Microwave and infrared spectra of HF–HCl and HCl–HF have been obtained using a molecular-beam electric-resonance optothermal spectrometer, which operates by quadrupole-field focusing of polar molecules onto a bolometer detector. The HF–HCl microwave measurements extend to Ka=1, the previous Ka=0 results of Janda, Steed, Novick, and Klemperer, allowing the determination of the Ka dependence and asymmetry of the Cl quadrupole coupling constant. For the metastable HCl–HF isomer no previous spectroscopic measurements have been reported. Here, microwave spectra are observed for the Ka=0 and 1 states and interpreted in terms of an L-shaped hydrogen-bonded structure for the complex, with a 3.235 A(ring) center-of-mass separation between the HF and HCl subunits. The DJ distortion constant indicates that the harmonic stretching force constant for HCl–HF is ∼35% larger than that of HF–HCl. Infrared spectra of the Ka=0–0 and 1–0 subbands of the H–F stretching band for HF–HCl and of the Ka=0–0 subband of the H–F stretch for HCl–HF are also reported. The vibrational predissociation linewidths depend on vibration, Ka state, isotopic species, and isomer excited.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457169
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  • 20
    Electronic Resource
    Electronic Resource
    Vibrational predissociation in the H–F stretching mode of HF–DF (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 633-636 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The high-resolution infrared spectrum of the K=1–0 subband of the H–F stretching vibrational band of the hydrogen-bonded HF–DF complex has been recorded using a molecular-beam electric resonance optothermal color-center-laser spectrometer. The spectrum exhibits minor perturbations and vibrational predissociation linewidths of 23±2 MHz full width at half-maximum for comparison to the 11±1 MHz widths found for the corresponding mode of the homonuclear HF–HF dimer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457168
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