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1.
The quantum numbers (J values and octahedral symmetry types) of the SF6 transitions from the ground state to v3 = 1 that fall within ± 1.5 G Hz of the CO2 P(14), P(18), and P(20) laser lines have been assigned. The SF6 absorptions nearest these three laser frequencies are R(28) A02, P(33) A12, and an F2 component of P(59) or P(60), respectively.  相似文献   

2.
Investigations are reported on the frequency characteristics of the cw high pressure CO2 laser and its use for high precision spectroscopy. The problem of using a cw tunable CO2 laser with a mixture of a few isotopes (12C16O2, 12C18O2, 12C16O18O and others) in a cw high pressure tunable CO2 laser is discussed. Broadening of the tuning range has given us the opportunity to find seven new absorption lines of SF6 near the transition P(20) of the 0001–1000 band of the CO2 laser.  相似文献   

3.
The absorption of CO2 laser pulses by low pressure SF6 gas has been investigated over a wide range of energy fluxes. For laser energy fluxes of 0.01–1 J cm-2 the effective absorption cross section varies between 0.2 and 2 × 10-18 cm2. For each laser line an individual dependence on the energy is found and in some cases minor changes in the absorption behaviour seem to occur around 0.1 J cm-2. SF6 excited with an average vibrational energy content of up to 20 photons/molecule does not absorb measurable amounts of 9.4 μm laser light. The influence of various SF6 and Ar pressures on the temporal shape of the transmitted pulses has been investigated.  相似文献   

4.
A band contour analysis is carried out for the ν3 absorption in SF6. Values of ΔB = ? (1.0 ? 1.5) × 10?4cm?1, ζ3 = 0.701, and ν0 = 948.2cm?1 are found. Tentative assignments are given for the SF6 rotational states which are pumped by the P(14) through P(22) lines of the CO2 laser.  相似文献   

5.
Enrichment of 34SF6 following irradiation of SF6?H2 mixtures by the focused output of a pulsed TEA CO2 laser has been studied as a function of the number of laser pulses, excitation wavelength, total pressure, and laser energy.  相似文献   

6.
Optically pumped vibrational transition lasing has been achieved for the first time in a nonlinear molecule. Laser radiation at 628.74 ± 0.02 cm?1 was generated from SF6 using CO2 TEA laser excitation. The SF6 pumping is shown to be via absorption of two photons.  相似文献   

7.
The linear absorption of CO2 laser radiation in SF6, WF6, and UF6 has been measured by using optoacoustic detection techniques. Absolute absorption coefficients per Torr as low as 1 × 10?7 cm?1 Torr?1 in a 2-cm active path length could be measured by taking advantage of calibration measurements performed with SF6.  相似文献   

8.
In a double-resonance experiment, the absorption of various CO2 laser lines by sulfur hexafluoride was measured, before and after the SF6 was pumped by a fixed frequency CO2 laser to a level of 5 quanta/molecule. The absorption is substantially shifted to longer wavelengths. But the short wavelength wing of the absorption band is not completely bleached. Instead a shoulder of several cm−1 width is left. This shoulder is probably important for the explanation of the infrared laser induced dissociation of SF6.  相似文献   

9.
The dissociation probabilities of32SF6 and some of34SF6 have been measured at a large number of CO2 laser lines both at room temperature and at 140 K. The longwavelength wing of this dissociation spectrum is exponential in the wavenumber. Its logarithmic slope is proportional to the inverse temperature. Selectivities are high enough at 140 K, that the photons are consumed only for the rare isotope in the case of34SF6 and nearly so for36SF6. For33SF6 further improvement of the selectivity would be desirable.  相似文献   

10.
Dissociation of 32SF6 and the resultant isotopic enrichment of 34SF6 using high-powered CO2 laser radiation has been studied with higher experimental sensitivity than previously reported. Enrichment factors have been measured as a function of laser pulse number, wavelength, energy and time duration. A geometry-independent dissociation cross section is introduced and measured values are presented. Threshold energy densities, below which no dissociation was observed, were also determined.  相似文献   

11.
The effect of mode locking on the CO2 laser-induced reaction of SF6 is reported. A mode-locked laser pulse enhances the SF6 reaction yield by a small (8%) but significant amount. The mode-locked pulse also decreases the isotopic selectivity of the reaction. This small effect is greater for enrichment of 33SF6 than for 34SF6. These results suggest that absorption mechanisms that have high power dependence play a minor role in the multiple-photon reaction.  相似文献   

12.
6 in flow with Ar (SF6: Ar=1:100) in conditions of a large vibrational/rotational temperature difference (TV≃230 K, TR≃60 K) was studied at moderate energy fluences from ≃0.1 to ≃100 mJ/cm2, which are of interest for isotope selective two-step dissociation of molecules. A 50 cm Laval-type slit nozzle for the flow cooling, and a TEA CO2-laser for excitation of molecules were used in the experiments. The laser energy fluence dependences of the SF6 MPA were studied for several CO2-laser lines which are in a good resonance with the linear absorption spectrum of the ν3 vibration of SF6 at low temperature. The effect of the laser pulse duration (intensity) on MPA of flow cooled SF6 with Ar was also studied. The results are compared with those obtained in earlier studies. Received: 4 September 1995/Revised version: 15 February 1996  相似文献   

13.
Measurements in SF6?H2 mixtures of HF1 fluorescence at 2.8 μm induced by pulsed CO2 laser radiation are reported. The dependence of fluorescence intensity on laser fluence is found to be strongly affected by the laser beam geometry in the interaction region. Our results show that the technique of HF1 fluorescence intensity detection can be a sensitive and reliable single-shot measure of multiple-photon dissociation of SF6 in a collisionless regime on condition that the laser fluence is uniform along the interaction region which is monitored.  相似文献   

14.
We present a grid of absolute reference frequencies based on CO2 (or N2O) lasers locked to saturation peaks of heavy molecules. Frequency differences between OsO4 peaks corresponding to adjacent CO2 laser lines from P(12) to P(22) have been measured with 1 kHz accuracy. This set includes one 192OsO4 resonance whose absolute frequency is known with the same accuracy. This absolute grid is then used to provide an absolute calibration of the ν3 band saturation spectrum of SF6. We also find a 23 kHz average frequency difference between the CO2 grid and the new OsO4 grid which we interpret tentatively as a small extrapolation error from the R to the P branch frequencies of CO2.  相似文献   

15.
IR photo-dissociation spectra of SF6 clusters have been studied. A He-seeded molecular beam has been attenuated by crossing it with a line tunable cw CO2 laser of moderate power. — In the electron bombardment beam ionizer (E el=100eV) small neutral clusters are found to fragment predominantly to the main monomer mass (SF 5 + ). — Predissociation spectra have been calculated for clusters containing up to six SF6-molecules invoking the dipole-dipole resonance force to lift the degeneracy of the molecule — excited molecule interaction. On the basis of these spectra, dimer and trimer concentrations have been determined quantitatively, for different molecular beam conditions.  相似文献   

16.
Theoretical predictions of collisionless multiphoton absorption in low temperature SF6 are presented and used to interpret the results of two recent experiments. Three major peaks in the experimental multiphoton absorption spectrum at 30 K, measured by Alimpiev and coworkers, are confirmed as being two-photon resonances to the A1g, Eg and F2g sub-states of 2v3. The measurements by Apatin and coworkers of multiphoton-induced depletion of rotational sub-levels of the ground vibrational state show excellent agreement with theory at the P(16) CO2 laser line, but the present theoretical framework is unable to account for the considerable depletion found experimentally at the P(24) and P(28) lines.  相似文献   

17.
Low pressure SF6 with its isotopes in natural abundance was irradiated by a pulsed CO2 laser operated on theP20 line (10.6 μm band). Dissociation yields of32SF6 and34SF6 were measured separately. If the radiation is focussed into the cell, the dissociation yield is proportional to the 3/2 power of the laser energy, as was derived under general conditions and confirmed experimentally. The reaction probabilityP(Φ), the fraction of molecules dissociated by an energy flux Φ, was measured using parallel light. For both isotopes,P(Φ) saturates at high energy flux close toP=1. At a lower flux (2 J cm−2), the dissociation probability of32SF6 displays a threshold, whereas the dissociation probability of34SF6 is a very steep function of Φ over the whole range of fluxes.P(Φ) at the higher energy flux was measured in a cavity absorption cell, in which up to 80% of the molecules were dissociated by a single pulse. Below 0.2 mbar SF6 the dissociation yields for both isotopes are pressure independent. Above 2 mbar the isotopic selectivity is completely lost. Addition of hydrogen always decreases the dissociation yields.  相似文献   

18.
First experiments on the infrared multiple-photon dissociation with ion molecules in beams have been carried out. A mass selected beam of SF+5 parent ions is crossed with a focused pulsed CO2 laser beam. Using mass spectroscopy for the detection, fragmentation into SF+4 and SF+3 has been observed. The relative yield and power dependence have been measured. Features of the MPD of ions in beams are discussed.  相似文献   

19.
A temperature measurement technique using SF6 molecules as tiny probe thermometers is described, and results are presented, for large (CO2) N van der Waals clusters (with N ≥ 102) in a cluster beam. The SF6 molecules captured by (CO2) N clusters in crossed cluster and molecular beams sublimate (evaporate) after a certain time, carrying information about the cluster velocity and internal temperature. Experiments are performed using detection of these molecules with an uncooled pyroelectric detector and infrared multiphoton excitation. The multiphoton absorption spectra of molecules sublimating from clusters are compared with the IR multiphoton absorption spectra of SF6 in the incoming beam. As a result, the nanoparticle temperature in the (CO2) N cluster beam is estimated as T cl < 150 K. Time-of-flight measurements using a pyroelectric detector and a pulsed CO2 laser are performed to determine the velocity (kinetic energy) of SF6 molecules sublimating from clusters, and the cluster temperature is found to be T cl = 105 ± 15 K. The effects of various factors on the results of nanoparticle temperature measurements are analyzed. The potential use of the proposed technique for vibrational cooling of molecules to low temperatures is discussed.  相似文献   

20.
The dissociation of NH3 into electronic ground-state fragments NH2(2B1) + H by high-intensity CO2 laser radiation has been observed under essentially collision free conditions and as a function of NH3 pressure, using laser fluorescence excitation for the NH2 detection. Luminescence from excited NH2 (2A1) produced directly by the CO2 laser has also been observed. The relative yield of NH2 (2A1) is estimated to be smaller than that of NH2 (2B1) by several orders of magnitude.  相似文献   

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