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  • 1
    Electronic Resource
    Electronic Resource
    A combined analysis of the ν9 band and the far-infrared torsional spectra of ethane (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 9609-9617 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Fourier transform measurements of the lowest frequency degenerate fundamental band of CH3CH3 (v9=1←0) in the 12-μm region together with far-infrared torsional spectra have been analyzed to investigate vibration–torsion–rotation effects in a symmetric top molecule. Several spectra of the ν9 band were recorded under different experimental conditions with apodized slit functions of about 0.002 cm−1. Although the intrinsic tunneling splitting in each (J′←J″) doublet in the ν9 band is predicted to be of the order of 0.002 cm−1, in some cases the observed splitting for an intermediate J″ of 20 is several times this value. In extreme cases, splittings of the order of 0.25 cm−1 have been observed. These splittings are caused primarily by the Coriolis interaction between the torsional stack of levels v4=0,1,2,..., for v9=1 and the corresponding stack for the ground vibrational state. Because of a near-degeneracy between the upper level in the ν9 band and its interacting partner (v9=0, v4=3), the (l=−1;K=17,σ=0) torsion–rotation series is resonantly perturbed. For this case, perturbation-allowed v4=3←0 torsional transitions have been identified. Here σ=0, 1, 2, or 3 labels the torsional sublevels. Measurements from the ν9 and 3ν4 bands, frequencies from the far-infrared torsional spectra in the ground vibrational state, and lower state combination differences from ν9+ν4−ν4 band were fitted to within experimental uncertainty using a symmetry adapted effective Hamiltonian which has been used for analyses of similar spectra in methyl silane and CH3CD3. Two Coriolis parameters were determined: the experimental value of ζ˜9z=0.2610(12) is in good agreement with the calculated value of 0.25, whereas the experimental value of ζ˜4,9x=0.2267(20) is about 3 times smaller than the calculated value of 0.60. The theoretical treatment presented here makes use of standard symmetric top formalism and the G36† double-group formalism. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480294
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  • 2
    Electronic Resource
    Electronic Resource
    Infrared diode laser spectroscopy of the CCO radical: The 2ν1−ν1 and ν1+ν3−ν3 difference bands (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 6588-6593 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The 2ν1−ν1 and ν1+ν3−ν3 difference bands of the CCO radical in the gas phase have been studied using a tunable infrared diode laser spectrometer. The CCO radical was produced using a flowing mixture of carbon suboxide and helium subjected to a hollow-cathode discharge. The spectral region between 1920–1960 cm−1 was probed. Ninety and seventy-five rovibrational transitions were measured in the 2ν1−ν1 and ν1+ν3−ν3 bands, respectively. The analyses of these bands yielded spectroscopic constants for the (001), (200), and (101) vibrational states. The band origins for 2ν1−ν1 and ν1+ν3−ν3 were determined to be 1941.85761(54) cm−1 and 1936.79402(56) cm−1, respectively. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476073
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  • 3
    Electronic Resource
    Electronic Resource
    Infrared laser spectroscopy of CCO: The ν1 band of the a˜1Δ electronic state (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 955-959 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The rotationally resolved infrared spectrum of the ν1 band of the long-lived a˜1Δ electronic state of the CCO radical has been observed between 1918 and 1970 cm−1 using a tunable diode laser spectrometer. Metastable CCO was produced in a discharge through a flowing mixture of carbon suboxide and helium. Fifty eight rovibrational transitions in the P and R branches and the five lowest J lines in the Q branch were measured. The band origin was determined to be 1942.8515(19) cm−1. This is in close agreement to the values determined previously from photoelectron spectroscopy of CCO−. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478140
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  • 4
    Electronic Resource
    Electronic Resource
    Vibration–torsion–rotation analysis of the ν12 band of CH3CD3 (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 838-848 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A Fourier transform spectrum of the lowest frequency degenerate fundamental of CH3CD3 (v12=1←0) near 680 cm−1 has been measured in order to investigate the vibration–torsion–rotation effects in a symmetric top. The spectrum was recorded at an instrumental resolution of 0.0024 cm−1 using a modified Bomem spectrometer. The temperature and pressure of the sample were 130 K and 0.4 Torr, respectively. Although the intrinsic tunneling splittings in each (J′←J″) multiplet are the order of 0.002 cm−1 or smaller, the splittings typically observed for an intermediate J″ of 10 are two to three orders of magnitude larger. These splittings are caused primarily by the Coriolis interaction between the torsional stack of levels v6=0,1,2,... for v12=1 and the corresponding stack for v12=0. The shift of each upper level (v12=1, l; J, v6=0, K, σ) is seen to be a sensitive function of (l;K,σ), where σ labels the torsional sublevels. Because of near degeneracies between the upper level and its interaction partner with (v12=0, v6=3), four different (l;K,σ) torsion–rotation series are resonantly perturbed. For three of these cases, perturbation-allowed (v6=3←0) torsional transitions have been identified. Over 2000 transitions belonging to the ν12 and 3ν6 bands have been assigned. The measurements from the present experiment and frequencies from previously reported studies in the ground vibrational state were fitted to within experimental uncertainty using an effective Hamiltonian discussed earlier in connection with CH3SiH3 [Moazzen-Ahmadi et al., J. Mol. Spectrosc. 137, 166 (1989)]. Several Coriolis parameters were determined. In particular, the experimental value of ζ˜12z=0.248 657(50) is in good agreement with the calculated value of 0.24, whereas the experimental value of ζ˜6,12x=0.2245(45) is in clear disagreement with the calculated value of 0.56. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475350
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  • 5
    Electronic Resource
    Electronic Resource
    Infrared diode laser spectroscopy of the ν3 fundamental and ν3+ν5−ν5 sequence bands of the C4 radical in a hollow cathode discharge (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 4033-4038 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The infrared absorption spectrum of the linear C4 radical has been studied in an extension of the original observation of gas-phase C4 by Heath and Saykally [J. Chem. Phys. 94, 3271 (1991)]. The experiment was performed using a flowing mixture of acetylene and helium subjected to a hollow-cathode discharge, which was probed in the 1525–1570 cm−1 spectral region using a tunable diode laser spectrometer. Transitions with N-values up to 60 were measured. Their analysis yielded band origins, rotational, and centrifugal distortion parameters for the lower and upper vibrational states, and l-type doubling parameters for the degenerate bending states ν5 and ν3+ν5. In particular, the ν3 origin was determined to be 1548.6128(4) cm−1, the ground state rotational and centrifugal distortion parameters were B=4979.89(21) MHz and D=0.848(44) kHz, and the l-doubling parameters for ν5 was q5=10.98(13) MHz. This value for q5 was used to estimate the ν5 frequency of gas-phase C4 to be 160±4 cm−1. Both the l=0 and 2 components of the ν3+2ν5−2ν5 sequence band were also tentatively observed, but a detailed analysis was not yet possible. The results were completely consistent with a linear structure for the triplet ground state of C4, and showed no effects of quasilinearity such as that exhibited by C3.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466340
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  • 6
    Electronic Resource
    Electronic Resource
    The torsional spectrum of CH3CH3 (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 563-577 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The perturbation-allowed torsional spectrum of gaseous CH3CH3 has been measured between 225 and 340 cm−1 at a resolution of 0.015 cm−1 using a Fourier transform spectrometer. The absorption path length was 124 m; the gas temperature and pressure were 295 K and 107 Torr, respectively. The P, Q, and R branches have been observed for all four torsional sublevels in the bands v4=1←0 and 2←1. A torsion–rotation Hamiltonian containing seven parameters was used to analyze 204 frequencies assigned in the P and R branches of the two bands. Effective values were obtained for the reduced rotational constant AR, the two leading coefficients V3 and V6 in the Fourier expansion of the hindering potential, the B rotational constant, and three distortion parameters. Estimates for the three zeroth order torsional parameters free of higher order contributions are: AR =2.6711(50) cm−1, V3=1012.0(1.0) cm−1, and V6=10.71(0.60) cm−1. The torsional energies calculated from the current model are compared to those obtained by earlier experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454183
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  • 7
    Electronic Resource
    Electronic Resource
    Millimeter-wave spectrum of CH3CD3 in the three lowest torsional states (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 2429-2438 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The pure rotational spectra of CH3CD3 in the three lowest torsional states has been observed using a mm-wave spectrometer. A total of 87 rotational frequencies were measured between 230–363 GHz for J=7←6 to 11←10 in v6=0, 1, and 2, where v6 is the torsional quantum number. For the lowest two torsional states, the spectra have the classic form expected for a symmetric top (with no internal rotation) in the ground vibrational state. For v6=2 and for a given (J+1)←J, a markedly different splitting pattern is observed as a result of the (K,σ) dependence of the effective rotational constant Bˆ, where σ labels the torsional sublevels. In order to identify the individual features in the (v6=2) spectrum, an assignment procedure was developed which is based on the fact that the ratio of moment of inertia of the top about the molecular symmetry axis to that of the whole molecule about the same axis is to a very good approximation 1/3. The torsion–rotation Hamiltonian discussed earlier in connection with CH3SiH3 [N. Moazzen-Ahmadi et al. J. Mol. Spectrosc. 119, 299 (1986)] was used to analyze the rotational frequencies along with the molecular beam anticrossing data and the origin of the torsional fundamental. Several constants which characterize the J-dependence of the energy levels were determined. Effective values for the barrier height V˜3 and the shape parameter V˜6 associated with the first-order correction in the Fourier expansion of the potential function were obtained. The effect of redundancies on the interpretation of the measurements is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465257
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  • 8
    Electronic Resource
    Electronic Resource
    Diode laser spectroscopy of gas phase C5: The ν3 fundamental and associated hot bands (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 2140-2147 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The spectrum of the linear carbon chain molecule C5 in the gas phase has been studied around 2170 cm−1, the region of the highest asymmetric stretching vibration ν3. The results were obtained using a tunable diode laser spectrometer and a cooled hollow cathode discharge in a flowing mixture of acetylene and helium. Four vibration–rotation bands were assigned and analyzed: the fundamental, a hot band arising from the v7=1, l=1 vibrational level, a second hot band arising from v7=2, l=0, and a third hot band tentatively ascribed to v5=1, l5=1. Small local perturbations were found to affect the upper vibrational states of two of the bands. Analysis of the data yielded accurate values for a number of molecular parameters for C5, e.g., the band origin ν3= 2169.4410(2) cm−1, the rotational constant, B0 =2557.63(9) MHz, and the l-type doubling parameters, q7=3.99(6) MHz, and q5=2.36(9) MHz. The value of q7 may be used to estimate a value of 118 cm−1 for the lowest bending frequency of the molecule. There is no evidence in C5 for quasilinear behavior such as that shown by C3 and C3O2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457073
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  • 9
    Electronic Resource
    Electronic Resource
    The torsional spectrum of CD3CD3 (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 2387-2394 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The far-infrared spectrum of gaseous CD3CD3 has been measured in the region of the torsional fundamental under relatively large pressure-path length conditions. The observations were made using a modified Bomem spectrometer at a resolution of 0.016 cm−1, an absorption path of 20 m, and a gas temperature and pressure of 168 K and 80 Torr, respectively. The prominent features of the spectrum are the P, Q, and R branches of the torsional fundamental (v4=1←0) and the Q branch of the first torsional overtone (v4=2←1). The P and R branches of the fundamental consist of peaks about 0.2 cm−1 wide due to unresolved structure. In addition, a very high resolution (0.0014 cm−1) spectrum of the lowest lying degenerate fundamental ν9 of CD3CD3 was obtained. From the combined intensity and frequency analyses of the far-infrared spectrum and 442 lower state combination differences in ν9 and its associated hot band ν9+ν4−ν4, the effective leading coefficients V˜3=989.10(68) cm−1 and V˜6=9.47(29) cm−1 in the Fourier expansion of the hindering potential were determined. The rotational constant B was found to be 13 802.658(39) MHz and four distortion parameters were obtained. The torsional dipole constants μ⊥ and μ(parallel)−μ⊥ were determined to be 7.41(74) and −19.9(2.0) μD, respectively. The experimental values of μ⊥ and μ(parallel)−μ⊥ are shown to be in good agreement with values calculated from theoretical expressions. The shape of the torsional bands can be reproduced in detail with the model adopted here.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459862
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  • 10
    Electronic Resource
    Electronic Resource
    Observation of the ν3 fundamental bands of HOSi+ and DOSi+ (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 5313-5315 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ν3 (O–Si stretch) fundamental bands of the HOSi+ and DOSi+ molecular ions in the 9 μm region have been detected for the first time, using a tunable infrared diode laser spectrometer and a hollow cathode discharge cell. Analysis of the results yielded accurate values for the molecular rotational and centrifugal distortion parameters, as well as for the band origins, which are 1127.009 cm−1 for HOSi+ and 1103.112 cm−1 for DOSi+ . The ground vibrational state parameters are in excellent agreement with those determined from the ν1 bands of the two isotopes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457633
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