首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 46 毫秒
1.
Jet-cooled fluorescence excitation and dispersed fluorescence spectra of 9-methylanthracene (MA), 9-cyanoanthracene (CA) and 9-cyano-10-methylanthracene (CMA) have been measured. The spectra of MA and CMA near the S0-S1 origin reveal a prominent torsional progression due to the hindered methyl group rotation and its torsional vibration against the aromatic ring frame. Additionally, the laser induced fluorescence LIF excitation spectrum of CMA shows the splitting of many vibrational modes.Observed positions and relative intensities of the methyl internal rotational bands were interpreted in terms of transitions calculated based on the quantum mechanical one-dimensional rotor. The low-frequency vibrational bands were interpreted also with the all electron quantum mechanical calculations within the RHF/6-31G(d,p), CIS/3-21G and CIS/6-31G(d,p) approximations. It is predicted that in the case of MA the eclipsed geometry (one C-H in the plane of the ring) is most stable in both S0 and S1 states. Conformation of the methyl group in CMA is suggested to change upon S1 ← S0 excitation (π/12 phase shift of the methyl group). The predicted energy barrier for methyl group rotation in the S0 state of CMA is considerably higher (72 cm−1) than that in the S1 state (22 cm−1). Following the present quantum mechanical calculations, the carbon atom of the methyl group belongs to the aromatic plane in the S0 ground state but it deviates from this plane in the S1 excited state. These in turn suggest that the calculated barrier for methyl group rotation in CMA has a 6-fold symmetry in the S0 ground state and roughly a 4-fold symmetry in the S1 state.  相似文献   

2.
The 3A2(nπ*)→1A1X (T1S0) phosphorescence excitation spectrum of jet-cooled xanthione was investigated in the region 14 920-17 600 cm−1. The structure observed is shown to be due to the T1S0 absorption and an assignment in terms of the vibronic structure of that band is proposed. A previous assignment of the S1S0 origin is considered in detail and the transition involved is shown to be most probably due to absorption of a vibronic triplet state T1z,ν7. An alternative but tentative assignment of the S1,0S0,0 transition is suggested. Comparison is made with previous spectroscopic and theoretical work on the molecule and its congeners, 4H-pyran-4-thione and 4H-1-benzopyran-4-thione.  相似文献   

3.
The absorption spectrum of ozone, 16O3, has been recorded in the 5903-5960 cm−1 region by high sensitivity CW-cavity ring down spectroscopy (αmin ∼ 5 × 10−10 cm−1). The ν1 + 3ν2 + 3ν3 and 4ν1 + ν2 + ν3 A-type bands centred at 5919.15 and 5947.07 cm−1 were newly observed. A set of 173 and 168 energy levels could be experimentally determined for the (1 3 3) and (4 1 1) states, respectively. Except for a few Ka = 5 levels of the (4 1 1) state, the rotational structure of the two states was found mostly unperturbed. The spectroscopic parameters were determined from a fit of the corresponding line positions by considering the (1 3 3) and (4 1 1) states as isolated. The determined effective Hamiltonian and transition moment operators were used to generate a list of 785 transitions given as Supplementary Material.  相似文献   

4.
The spectra of the gaseous mixtures CH4-He and CH4-Ar were obtained in the spectral region 1400-1750 cm−1 with a resolution up to 0.003 cm−1. Helium and argon pressure broadenings for the vibration-rotation lines of the ν2 band of CH4 have been estimated at room temperature for some lines in the P, Q, and R branches. These values were also calculated using the theoretical approach developed by Robert and Bonamy, extended to the case of tetrahedral molecules. The helium data have been found to be in a satisfactory agreement whereas a divergence of calculated and measured broadening coefficients has been evidenced in the case of argon. Simulations of the ν2 band shapes of methane perturbed by helium have also been performed.  相似文献   

5.
This sixth of a series of publications on the high-resolution rotation-vibration spectra of sulfur trioxide reports the results of a systematic study of the ν3 and 2ν3 infrared bands of the four symmetric top isotopomers 32S16O3, 32S18O3, 34S16O3, and 34S18O3. An internal coupling between the l=0(A1) and l=2(E) levels of the 2ν3 states was observed. This small perturbation results in a level crossing between |kl|=9 and 12, in consequence of which the band origins of the A1,l=0 “ghost” states could be determined to a high degree of accuracy. Ground and upper state rotational constants as well as vibrational anharmonicity constants are reported. The constants for the center-of-mass substituted species 32S16O3 and 34S16O3 vary only slightly, as do the constants for the 32S18O3, 34S18O3 pair. The S-O bond lengths for the vibrational ground states of the species 32S16O3, 34S16O3, 32S18O3, and 34S18O3 are, respectively, 141.981 99(1), 141.979 38(6), 141.972 78(8), and 141.969 93(8) pm, where the uncertainties, given in parentheses, are two standard deviations and refer to the last digits of the associated quantity.  相似文献   

6.
We report high resolution infrared absorption studies of rare gas (Rg) atom doped solid parahydrogen in the hydrogen S1(0) region around 4486 cm−1. At low Rg atom concentrations (∼0.1%), satellite transitions appear in the S1(0) region due to rovibrational excitation of parahydrogen molecules with one nearest-neighbor Rg atom. The Ne satellite feature differs qualitatively from the Ar, Kr, and Xe satellite features for reasons described within. The frequency of the S1(0) satellite features linearly shift to lower energy as the polarizability of the Rg atom increases while the absorption coefficients increase with the square of the Rg atom polarizability. Rotational calculations are performed for H2 with a nearest-neighbor Rg atom assuming a rigid hexagonal close-packed lattice structure. The calculated fine structure of the S1(0) satellite features agree qualitatively with lifting of the 2J+1 degeneracy of the v = 1, J = 2 upper state caused by the anisotropy in the Rg-H2 intermolecular potential. The discrepancy between the calculated and measured Rg atom S1(0) satellite features may signal partial delocalization of the J = 2 roton onto neighboring parahydrogen molecules.  相似文献   

7.
Rotationally resolved ultrahigh-resolution fluorescence excitation spectra of the S1 ← S0 transition of dibenzofuran have been observed using the technique of crossing a collimated molecular beam and the single-mode UV laser beam. 3291 rotational lines of the band and 3047 rotational lines of the band have been assigned. The band has been found to be a b-type transition, in which the transition moment is along the twofold symmetry axis of this molecule, and only the ΔKa = ± 1 transitions were observed. The excited state is identified to be the S11A1(ππ) state. In contrast with this, the band has been found to be an a-type transition in which the transition moment is along the long axis in plane. It indicates that the intensity of this vibronic band arises from vibronic coupling with the S21B2(ππ) state. We determined the accurate rotational constants and the molecule have been shown to be planar both in the ground and excited states.  相似文献   

8.
Rotational spectra have been observed for BiO produced in a DC discharge through a low pressure mixture of O2, Ar, and Bi vapor. Because of the highly non-thermal distribution of states, it has been possible to observe spectra arising from the X12Π1/2 level up to v = 9 and for the X22Π3/2 level up to v = 5 near 10 538 cm−1. Precise rotational and hyperfine parameters have been determined for the observed states. By using available near infrared (NIR) data in a merged fit, the 0-0 and 1-1 fine structure intervals have been more precisely determined. Although the quality of the fit is very good, the interpretation of the hyperfine constants is complicated by relativistic effects and the interaction of the X2 state with A14Π3/2 state. The magnetic and quadrupole coupling constants will be compared with those of the Bi atom and related molecules.  相似文献   

9.
We report measured Lorentz O2-broadening and O2-induced pressure-shift coefficients of CH3D in the ν2 fundamental band. Using a multispectrum fitting technique we have analyzed 11 laboratory absorption spectra recorded at 0.011 cm−1 resolution using the McMath-Pierce Fourier transform spectrometer, Kitt Peak, Arizona. Two absorption cells with path lengths of 10.2 and 25 cm were used to record the spectra. The total sample pressures ranged from 0.98 to 339.85 Torr with CH3D volume mixing ratios of 0.012 in oxygen. We report measurements for O2 pressure-broadening coefficients of 320 ν2 transitions with quantum numbers as high as J″ = 17 and K = 14, where K″ = K′ ≡ K (for a parallel band). The measured O2-broadening coefficients range from 0.0153 to 0.0645 cm−1 atm−1 at 296 K. All the measured pressure-shifts are negative. The reported O2-induced pressure-shift coefficients vary from about −0.0017 to −0.0068 cm−1 atm−1. We have examined the dependence of the measured broadening and shift parameters on the J″, and K quantum numbers and also developed empirical expressions to describe the broadening coefficients in terms of m (m = −J″, J″, and J″ + 1 in the QP-, QQ-, and QR-branch, respectively) and K. On average, the empirical expressions reproduce the measured broadening coefficients to within 4.4%. The O2-broadening and pressure shift coefficients were calculated on the basis of a semiclassical model of interacting linear molecules performed by considering in addition to the electrostatic contributions the atom-atom Lennard-Jones potential. The theoretical results of the broadening coefficients are generally larger than the experimental data. Using for the trajectory model an isotropic Lennard-Jones potential derived from molecular parameters instead of the spherical average of the atom-atom model, a better agreement is obtained with these data, especially for |m| ? 12 values (11.3% for the first calculation and 8.1% for the second calculation). The O2-pressure shifts whose vibrational contribution are either derived from parameters fitted in the QQ-branch of self-induced shifts of CH3D or those obtained from pressure shifts induced by Xe in the ν3 band of CH3D are in reasonable agreement with the scattered experimental data (17.0% for the first calculation and 18.7% for the second calculation).  相似文献   

10.
The high-resolution Fourier transform absorption spectrum of an isotopic sample of nitrogen dioxide, 15N16O2, was recorded in the 3.4 μm region. Starting from the results of a previous study [Y. Hamada, J. Mol. Struct. 242 (1991) 367-377] a new analysis of the ν1 + ν3 band located at 2858.7077 cm−1 has been performed. This new assignment concerns (1 0 1) energy levels involving rotational quantum numbers up to Ka = 10 and N = 54. Using a theoretical model which accounts for both the electron spin-rotation resonances within each vibrational state and the Coriolis interactions between the (1 2 0) and (1 0 1) vibrational states, the spin-rotation energy levels of the (1 0 1) vibrational state could be reproduced within their experimental uncertainty. In this way, the precise vibrational energy, rotational, spin-rotation, and coupling constants were achieved for the {(1 2 0), (1 0 1)} interacting states of 15N16O2. Using these parameters and the transition moment operator which was obtained for the main isotopic species, 14N16O2, a comprehensive list of the line positions and intensities was generated for the ν1 + ν3 band of 15N16O2.  相似文献   

11.
Emission spectra of the b1Σ+(b0+) → X3Σ(X10+,X21) and a1Δ(a2) → X21 transitions of AsBr have been measured in the near-infrared spectral region with a Fourier-transform spectrometer. The arsenic bromide radicals were generated in fast-flow systems by reaction of arsenic vapor (Asx) with bromine and were excited by microwave-discharged oxygen. The most prominent features in the spectrum are the Δv = +1,0,−1, and −2 band sequences of the b1Σ+(b0+) → X3Σ(X10+) transition in the range 11 700-12 700 cm−1. With lower intensities, the Δv = 0 and −1 sequences of the b1Σ+(b0+) → X3Σ(X21) sub-system show up in the same range. Further to the red, between 6000 and 6700 cm−1, the Δv = 0, +1, and −1 sequences of the hitherto unknown a1Δ(a2) → X21 transition are observed. Analyses of medium- and high-resolution spectra have yielded improved molecular constants for the X10+, X21, and b0+ states and first values of the electronic energy and the vibrational constants of the a2 state.  相似文献   

12.
High-resolution Fourier transform spectrum of phosphine (PH3) at room temperature has been recorded in the region of the 3ν2 band (2730-3100 cm−1) at an apodized resolution of 0.005 cm−1. About 200 vibration-rotation transitions have been least squares fitted with an rms of 0.00039 cm−1 after taking into account the ΔK = ±3 interaction.  相似文献   

13.
A high-resolution Fourier transform spectrum of the D2MSe species (M = 82, 80, 78, 77, and 76) in the region 2300-2500 cm−1 was recorded for the first time and assigned. On the basis of these experimental data, rotation-vibration energies of the (1 1 0) and (0 1 1) vibrational states were fitted, and band centers, and rotational, centrifugal distortion, and resonance interaction parameters were determined for the main D280Se species. The obtained set of 32 fitted parameters reproduces the 647 rotation-vibration energies with a rms deviation of 0.00024 cm−1. The ν1 + ν2 and ν2 + ν3 bands of the other four isotopic species are analyzed as well.  相似文献   

14.
The ammonia ν1 + 2ν4 perpendicular stretch-bend combination band has been investigated in spectra of 14NH3 and 15NH3 recorded in the 6400-6800 cm−1 region with an external cavity tunable diode laser (ECTDL) spectrometer. For 14NH3, new assignments were determined initially by extrapolating from published low-J jet-cooled beam results up to transitions of higher J and K. Corresponding ν1 + 2ν4 transitions for the 15NH3 species were then found by identifying similar patterns of lines with a characteristic downshift of approximately 9.7 cm−1. Assignments were confirmed employing ground-state combination differences. Term values, a-s inversion splittings, l-doubling energies and parameter estimates from simple single-state fits are reported for the two ammonia species.  相似文献   

15.
The saturation absorption technique is applied to the 87Rb 2S1/2 F″ = 2 → 2P3/2 F′ = 1, 2 and 3 transitions to study the effect of velocity changing collisions (VCC). The VCC caused Doppler pedestal increases with argon pressure from 0 to 110 mTorr and decreases with modulation frequencies of 700-3200 Hz. The resonances of the velocity selective, saturated optical pumping are washed out for pressure of 110 mTorr. The magnitude of the Doppler pedestal relative to the homogeneous features, yields a rate for velocity changing collisions of 6.5 ± 0.2 × 10−10 cm3 s−1.  相似文献   

16.
Antiferromagnetic phase transition in two vanadium garnets AgCa2Co2V3O12 and AgCa2Ni2V3O12 has been found and investigated extensively. The heat capacity exhibits sharp peak due to the antiferromagnetic order with the Néel temperature TN=6.39 K for AgCa2Co2V3O12 and 7.21 K for AgCa2Ni2V3O12, respectively. The magnetic susceptibilities exhibit broad maximum, and these TN correspond to the inflection points of the magnetic susceptibility χ a little lower than T(χmax). The magnetic entropy changes from zero to 20 K per mol Co2+ and Ni2+ ions are 5.31 J K−1 mol-Co2+-ion−1 and 6.85 J K−1 mol-Ni2+-ion−1, indicating S=1/2 for Co2+ ion and S=1 for Ni2+ ion. The magnetic susceptibility of AgCa2Ni2V3O12 shows the Curie-Weiss behavior between 20 and 350 K with the effective magnetic moment μeff=3.23 μB Ni2+-ion−1 and the Weiss constant θ=−16.4 K (antiferromagnetic sign). Nevertheless, the simple Curie-Weiss law cannot be applicable for AgCa2Co2V3O12. The complex temperature dependence of magnetic susceptibility has been interpreted within the framework of Tanabe-Sugano energy diagram, which is analyzed on the basis of crystalline electric field. The ground state is the spin doublet state 2E(t26e) and the first excited state is spin quartet state 4T1(t25e2) which locates extremely close to the ground state. The low spin state S=1/2 for Co2+ ion is verified experimentally at least below 20 K which is in agreement with the result of the heat capacity.  相似文献   

17.
This study provides the first direct experimental measurements of the off-diagonal relaxation matrix element coefficients for line mixing in air-broadened methane spectra for any vibrational band and the first off diagonal relaxation matrix elements associated with line mixing for pure methane in the ν2 + ν3 band of 12CH4. The speed-dependent Voigt profile with line mixing is used with a multispectrum nonlinear least squares curve fitting technique to retrieve the various line parameters from 11 self-broadened and 10 air-broadened spectra simultaneously. The room temperature spectra analyzed in this work are recorded at 0.011 cm−1 resolution with the McMath-Pierce Fourier transform spectrometer located at the National Solar Observatory, Kitt Peak, Arizona. The off-diagonal relaxation matrix element coefficients of ν2 + ν3 transitions between 4410 and 4629 cm−1 are reported for eighteen pairs with upper state J values between 2 and 11. The observed line mixing coefficients for self broadening vary from 0.0019 to 0.0390 cm−1 atm−1 at 296 K. The measured line mixing coefficients for air broadening vary from 0.0005 to 0.0205 cm−1 atm−1 at 296 K.  相似文献   

18.
A high resolution cavity ringdown spectrometer (CRDS) has been constructed using a 1.5 μm continuous-wave external-cavity tunable diode laser, a mode-matched near-confocal ringdown cavity, and 2 cm pulsed slit jet. Without signal averaging, the RMS noise in the absorption signal is 1.7 × 10−9 cm−1. The rotationally resolved overtone spectrum of the OH(ν1) + CH(ν3) stretch combination band of methanol between 6510 and 6550 cm−1 has been observed for J=0-8 and K=0-3 at sub-Doppler resolution. In total, 418 lines are assigned and global fits yield molecular torsion-rotation parameters for the upper state. Four K-localized perturbations are analyzed and the pattern of residuals is discussed.  相似文献   

19.
N2-broadening coefficients have been measured for 41 transitions of PH3 at −100 °C in the QR branch of the ν2 band and the PP, RP, and SP branches of the ν4 band, using a tunable diode-laser spectrometer. The recorded lines with J values ranging from 1 to 13 and K from 0 to 10 are located between 1026 and 1093 cm−1. The collisional widths are determined by fitting each spectral line with a Voigt profile, a Rautian profile, and a speed-dependent Rautian profile. The latter models provide larger broadening coefficients than the Voigt model. These coefficients have also been calculated on the basis of a semiclassical model of interacting linear molecules by considering an atom-atom Lennard-Jones potential in addition to the electrostatic contributions. By comparing broadening coefficients at room and low temperatures, the temperature dependence of these broadenings has been determined both experimentally and theoretically.  相似文献   

20.
The effects of temperature and pressure on the formation and decomposition of C6H5C2H2O2 in the C6H5C2H2 + O2 reaction have been investigated at temperatures from 298 to 378 K by directly monitoring the C6H5C2H2O2 radical in the visible region by cavity ringdown spectrometry (CRDS). The rate constant for the C6H5C2H2 + O2 association and that for fragmentation of C6H5C2H2O2 were found to be k1 (C6H5C2H2 + O2 → C6H5C2H2O2) = (3.20 ± 1.19) × 1011 exp(+760/T) cm3 mol−1 s−1 and k2 (C6H5C2H2 O2 → C6H5CHO + HCO) = (1.68 ± 0.13) × 104 s−1, respectively. Additional kinetic measurements by pulsed laser photolysis/mass spectrometry show that C6H5CHO was produced in the C6H5C2H2 + O2 reaction as predicted and the formation of C6H5CHO from the decomposition of C6H5C2H2O2 is temperature-independent, consistent with the CRDS experimental data.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号