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  • 1
    Digitale Medien
    Digitale Medien
    Far-infrared spectrum of N2 and N2-noble gas mixtures near 80 K (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 3511-3516 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The far-infrared absorption spectra of gaseous nitrogen, and mixtures of nitrogen with the foreign gases argon and neon, have been measured at pressures near 1 atm. and at temperatures near 78 and 89 K. Spectra were obtained over the wave number range 20–100 cm−1 using a Fourier transform spectrometer and a multiple reflection absorption cell of 52 m path length. They show a broad continuum associated with the pure rotational collision-induced S branch of the N2 molecule plus structure attributed to transitions in dimers, not previously observed in this spectral region. In the case of N2–Ar, there are strong similarities with the fundamental vibrational band under similar conditions of pressure and temperature as reported by McKellar [J. Chem. Phys. 88, 4190 (1988)]. The integrated absorption coefficient has been evaluated for the N2–N2 rotational band; at 78 K it equals 3.1×10−31 cm5 sec−1, a factor of 2 greater than typical values at temperatures above 100 K. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.471056
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  • 2
    Digitale Medien
    Digitale Medien
    Hyperfine-resolved rovibrational spectrum of the X 2Π state of HI+ (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 8725-8735 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: A high resolution spectroscopic study of HI+ has been carried out for the first time. The absorption spectrum in the inverted 2Π ground electronic state has been measured with a linewidth of 0.004 cm−1 between 1995 and 2245 cm−1. A total of 117 vibration–rotation transitions were observed with a tunable diode laser spectrometer coupled to an ac glow discharge cell employing velocity modulation. Lines were measured in the vibrational fundamental of the 2Π1/2 spin substate and in the three lowest (v+1←v) bands of the 2Π3/2 spin substate. A good fit to the data was obtained using a standard vibration–rotation, fine structure Hamiltonian. Equilibrium values were determined for 16 molecular parameters including the harmonic vibrational frequency ωe, the rotational constant Be, and the Λ-doubling constants pe and qe. A review of the ground state properties of the hydrogen halide ions HX+ (X=F, Cl, Br, I) shows that the harmonic force constant is, to excellent approximation, a linear function of the internuclear spacing. In ten different vibration–rotation transitions of the two spin substates of HI+, hyperfine splittings were observed. A total of 58 relative splittings of hyperfine components were analyzed to determine the iodine quadrupole coupling constant eQq0 as well as the Frosch–Foley magnetic hyperfine constants a, (b+c), and d. The results have been used to investigate the electronic properties of the ion. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.468976
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  • 3
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.454183
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  • 4
    Digitale Medien
    Digitale Medien
    The microwave rotational spectrum of the Ar–CO dimer (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 9399-9404 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Pure rotational spectra of four different isotopomers of the dimer Ar–CO have been investigated between 8 and 18 GHz using a pulsed beam cavity Fourier transform spectrometer. The spectra confirm that the complex is a prolate near-symmetric rotor with an essentially T-shaped structure, and that it undergoes large amplitude zero-point motion. It is shown that on the average the argon is closer to the oxygen than to the carbon. The transitions measured obey a-type selection rules with ΔJ=+1, ΔKa=0, and ΔKc=+1. For 40Ar–12C16O, transitions have been observed for Ka=0 and 1 with lower state J values of 1, 2, and 3. For 40Ar–13C16O and 40Ar–13C18O, a similar series was measured, but only for Ka=0. For 40Ar–13C17O, the 17O quadrupole hyperfine pattern was resolved in the rotational transition JKaKc = 202–101. Determinations have been made for rotational and centrifugal distortion constants, as well as for the 17O quadrupole coupling constant χaa. Effective values have been obtained for the length of the line from the center of mass of the CO subunit to the argon nucleus, and for the angle between this line and the CO bond.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.464371
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  • 5
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.465257
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  • 6
    Digitale Medien
    Digitale Medien
    Erratum: Two-photon microwave transitions within a two-level system [J. Chem. Phys. 92, 7128 (1990)] (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 831-831 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.460755
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  • 7
    Digitale Medien
    Digitale Medien
    High-resolution spectrum of the C–O stretch overtone band in methyl alcohol (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 7049-7053 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The Fourier-transform spectrum of the CH3OH overtone C–O stretching band (vCO=2←0) has been recorded in the range 1950–2060 cm−1, at a resolution of 0.004 cm−1. The spectrum is resolved into J multiplets, each displaying complicated substructure due to strong torsion–vibration–rotation effects. Within this structure, it has been possible so far to identify R and P branch transitions for K=0 and K=1 for both A and E torsional symmetry species for J≤24. The assignments are supported by combination differences derived from known ground-state frequencies. The identified branches have been analyzed in terms of effective state-dependent series-expansion parameters, and the leading terms in the torsion–rotation Hamiltonian have been derived for the second excited C–O stretching state. The vCO=2 torsional barrier height is obtained as 395.5±0.2 cm−1, and the effective B value as 23 671.9±1.3 MHz. In addition, the 34.946 cm−1 far-infrared laser line pumped by the 10R(48) CO2 laser line has been tentatively identified as the (nτK,J)v=(031+,16)2→(010+,15)2 transition, and its parent IR pump absorption as the P(031+,17) vCO=2←1 hot-band line.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.459427
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  • 8
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.459862
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  • 9
    Digitale Medien
    Digitale Medien
    Two-photon microwave transitions within a two-level system (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 7128-7134 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Two-photon pure rotational transitions in the symmetric top CF3CCH have been observed with a pulsed beam Fourier transform crossed-cavity spectrometer modified to allow the application of a static Stark field. Transient one-photon emission signals at ν0=17 267 MHz for transitions between the levels (J=3,K,M) and (2,K,M) are generated for KM≠0 by the application of intense pulses at ν0/2. It has been demonstrated that the two-photon transitions occur within an effectively isolated two-level system as a result of the first order ac Stark effect. Quantitative studies of the intensities as a function of pulse length and power show that the two-photon transition probability in the microwave region is well represented by the theoretical model used by Meerts, Ozier, and Hougen [J. Chem. Phys. 90, 4681 (1989)] to treat multiphoton transitions in a two-level system whose one-photon frequency is (approximately-less-than)1 MHz. A description is given of the spectrometer with emphasis on the modifications made for two-photon studies.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.458253
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  • 10
    Digitale Medien
    Digitale Medien
    A precise calibration system for high-resolution visible-laser spectroscopy (1989)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 60 (1989), S. 1003-1007 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A method for calibrating high-resolution laser spectra in the visible is described. The system is based on an evacuated Fabry–Perot étalon whose cavity length is servolocked to a stabilized HeNe laser; the absolute order number of the fringe at the HeNe frequency is known and the free spectral range can be determined with high accuracy. For absolute-frequency measurements the order number of a transmission fringe is obtained from a commercial wavemeter (whose accuracy is sufficient to identify the fringe); the absolute frequency is then the HeNe frequency multiplied by the ratio of the "unknown'' order number to the "lock-point'' order number. The long-term frequency reproducibility of the system is better than 25 MHz. Small-frequency splittings such as molecular hyperfine intervals can be measured to ±1 MHz, while large-frequency intervals (of the order of 500 GHz) are consistent to better than 10 MHz.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1140307
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