The effects of energy-level resonance on collision-induced electronic energy transfer: CD (A (2)Delta<--> B (2)Sigma(-)) coupling

Pulsed, time- and wavelength-resolved laser-induced fluorescence spectroscopy has been used to measure rate constants for collision-induced electronic energy transfer (EET) between the A (2)Delta and B (2)Sigma(-) states of the CD radical. EET rate constants in the exothermic direction from B (2)Sigma(-), v = 0 to the unresolved A (2)Delta, v = 0 and 1 levels span the range 0.1-2.4 x 10(-11) cm(3) s(-1) at room temperature (ca. 295 K) for the partners He, Ar, N(2), CO and CO(2). H(2) was also investigated, but was unsuitable for further study because of its rapid isotope exchange with CD(X (2)Pi). As expected, only CO results in a significant rate of removal on any distinct, unobserved channel, presumed to be chemical reaction. The efficient A (2)Delta, v = 1 --> 0 vibrational relaxation by CO(2) observed previously for CH was not found for CD. Despite the significant differences in their detailed rovibronic level structures, the overall efficiency of EET in CD was found to be very similar to that for CH. The positive correlation in a Parmenter-Seaver plot appears to confirm a role for long-range attractive forces in the EET process. However, the detailed deviations from this overall trend found reproducibly for CD and CH suggests that partner-specific interactions are also important.     

Kinetic study of vibrational energy transfer from a wide range of vibrational levels of O2(X(3)Sigma(g)-, v = 6-12) to CF4

A wide range of vibrational levels of O2(X(3)Sigma(g)(-), v = 6-13) generated in the ultraviolet photolysis of O3 was selectively detected by the laser-induced fluorescence (LIF) technique. The time-resolved LIF-excited B(3)Sigma(u)(-)-X(3)Sigma(g)(-) system in the presence of CF4 has been recorded and analyzed by the integrated profiles method (IPM). The IPM permitted us to determine the rate coefficients k(v)(CF4) for vibrational relaxation of O2(X(3)Sigma(g)(-), v = 6-12) by collisions with CF4. Energy transfer from O2 (v = 6-12) to CF4 is surprisingly efficient compared to that of other polyatomic relaxation partners studied so far. The k(v)(CF4) increases with vibrational quantum number v from [1.5 +/- 0.2(2sigma)] x 10(-12) for v = 6 to [7.3 +/- 1.5(2sigma)] x 10(-11) for v = 12, indicating that the infrared-active nu3 vibrational mode of CF4 mainly governs the energy transfer with O2(X(3)Sigma(g)(-), v = 6-12). The correlation between the rate coefficients and fundamental infrared intensities has been discussed based on a comparison of the efficiency of energy transfer by several collision partners.     

State-resolved dynamics of the CN(B2Sigma+) and CH(A2Delta) excited products resulting from the VUV photodissociation of CH3CN

Fourier transform visible spectroscopy, in conjunction with VUV photons produced by a synchrotron, is employed to investigate the photodissociation of CH3CN. Emission is observed from both the CN(B2Sigma+-X2Sigma+) and CH(A2Delta-X2Pi) transitions; only the former is observed in spectra recorded at 10.2 and 11.5 eV, whereas both are detected in the 16 eV spectrum. The rotational and vibrational temperatures of both the CN(B2Sigma+) and CH(A2Delta) radical products are derived using a combination of spectral simulations and Boltzmann plots. The CN(B2Sigma+) fragment displays a bimodal rotational distribution in all cases. Trot(CN(B2Sigma+)) ranges from 375 to 600 K at lower K' and from 1840 to 7700 K at higher K' depending on the photon energy used. Surprisal analyses indicate clear bimodal rotational distributions, suggesting CN(B2Sigma+) is formed via either linear or bent transition states, respectively, depending on the extent of rotational excitation in this fragment. CH(A2Delta) has a single rotational distribution when produced at 16 eV, which results in Trot(CH(A2Delta))=4895+/-140 K in v'=0 and 2590+/-110 K in v'=1. From thermodynamic calculations, it is evident that CH(A2Delta) is produced along with CN(X2Sigma+)+H2. These products can be formed by a two step mechanism (via excited CH3* and ground state CN(X2Sigma+)) or a process similar to the "roaming" atom mechanism; the data obtained here are insufficient to definitively conclude whether either pathway occurs. A comparison of the CH(A2Delta) and CN(B2Sigma+) rotational distributions produced by 16 eV photons allows the ratio between the two excited fragments at this energy to be determined. An expression that considers the rovibrational populations of both band systems results in a CH(A2Delta):CN(B2Sigma+) ratio of (1.2+/-0.1):1 at 16 eV, thereby indicating that production of CH(A2Delta) is significant at 16 eV.     

Spin-orbit coupling in O2(v)+O2 collisions: a new energy transfer mechanism

A reduced dimensionality model is used to study the relaxation of highly vibrationally excited O(2)(X (3)Sigma(g) (-),v>/=20) in collisions with O(2)(X (3)Sigma(g) (-),v=0). Spin-orbit coupled potential energy surfaces are employed to incorporate the vibrational-to-electronic energy transfer mechanism involving the O(2)(a (1)Delta(g)) and O(2)(b (1)Sigma(g) (+)) excited states. The transition probabilities obtained show a sharp increase for v>/=26 providing the first direct evidence of the important role played by the electronic energy transfer processes in the depletion of O(2)(X (3)Sigma(g) (-),v>/=26).     

Threshold-photoelectron-spectroscopy-coincidence study of the double photoionization of HBr

A threshold-photoelectron-coincidence spectrum of HBr has been recorded in the 32.2-35.8 eV photon energy range, with a resolution of approximately 0.01 eV, using a synchrotron radiation source. The X (3)Sigma(-) and a (1)Delta(2) states of the HBr(2+) dication are clearly observed in the spectrum, while there is no clear evidence for the formation of the b (1)Sigma(+) electronic state. For the first two states, the vibrational states v=0-3 have been resolved, while for the ground X (3)Sigma(-) state also spin-orbit splitting has been detected. The results appear in good agreement with previous experimental observations. A comparison with theoretical predictions indicates the role of "noncovalent" contributions to the interaction between the two atomic partners for the formation of metastable states.     

Photodissociation dynamics of IBr(-)(CO(2))(n), n<15

We report the ionic photoproducts produced following photoexcitation of mass selected IBr(-)(CO(2))(n), n=0-14, cluster ions at 790 and 355 nm. These wavelengths provide single state excitation to two dissociative states, corresponding to the A(') (2)Pi(1/2) and B 2 (2)Sigma(1/2) (+) states of the IBr(-) chromophore. Excitation of these states in IBr(-) leads to production of I(-)+Br and Br(-)+I( *), respectively. Potential energy curves for the six lowest electronic states of IBr(-) are calculated, together with structures for IBr(-)(CO(2))(n), n=1-14. Translational energy release measurements on photodissociated IBr(-) determine the I-Br(-) bond strength to be 1.10+/-0.04 eV; related measurements characterize the A(') (2)Pi(1/2)<--X (2)Sigma(1/2) (+) absorption band. Photodissociation product distributions are measured as a function of cluster size following excitation to the A(') (2)Pi(1/2) and B 2 (2)Sigma(1/2) (+) states. The solvent is shown to drive processes such as spin-orbit relaxation, charge transfer, recombination, and vibrational relaxation on the ground electronic state. Following excitation to the A(') (2)Pi(1/2) electronic state, IBr(-)(CO(2))(n) exhibits size-dependent cage fractions remarkably similar to those observed for I(2) (-)(CO(2))(n). In contrast, excitation to the B 2 (2)Sigma(1/2) (+) state shows extensive trapping in excited states that dominates the recombination behavior for all cluster sizes we investigated. Finally, a pump-probe experiment on IBr(-)(CO(2))(8) determines the time required for recombination on the ground state following excitation to the A(') state. While the photofragmentation experiments establish 100% recombination in the ground electronic state for this and larger IBr(-) cluster ions, the time required for recombination is found to be approximately 5 ns, some three orders of magnitude longer than observed for the analogous I(2) (-) cluster ion. Comparisons are made with similar experiments carried out on I(2) (-)(CO(2))(n) and ICl(-)(CO(2))(n) cluster ions.     

Observation and calculation of the Cs2 2 3Delta(1g) and b 3Pi(0u) states

The Cs(2) 2 (3)Delta(1g) and b (3)Pi(0u) states have been observed by infrared-infrared double resonance spectroscopy for the first time. 221 2 (3)Delta(1g)<--A (1)Sigma(u) (+)<--X (1)Sigma(g) (+) double resonance lines have been assigned to transitions into the 2 (3)Delta(1g) v=6-13 vibrational levels. Resolved fluorescence into the b (3)Pi(0u) v(')=0-48 levels has been recorded. Molecular constants and potential energy curves are determined by the global fit of the entire set of the experimental data. Theoretical potential energy curves of the 2 (3)Delta(g) and b (3)Pi(u) states have been determined in the framework of the pseudopotential method and are compared with the experimental results.     

Vibrational and rotational energy transfers involving the CH B 2Sigma(-) v=1 vibrational level in collisions with Ar, CO, and N2O

With photolysis-probe technique, we have studied vibrational and rotational energy transfers of CH involving the B (2)Sigma(-) (v=1, 0F(1) transitions are larger than the reverse F(1)-->F(2) transitions in DeltaN=0 for the Ar and CO collisions. The trend of fine-structure conservation is along the order of N(2)O相似文献   

Intra- and intermolecular vibrational energy transfer in tungsten carbonyl complexes W(CO)5(X) (X=CO, CS, CH3CN, and CD3CN)

Vibrational energy relaxation of degenerate CO stretches of four tungsten carbonyl complexes, W(CO)6, W(CO)5(CS), W(CO)5(CH3CN), and W(CO)5(CD3CN), is observed in nine alkane solutions by subpicosecond time-resolved infrared (IR) pump-probe spectroscopy. Between 0 and 10 ps after the vibrational excitation, the bleaching signal of the ground-state IR absorption band shows anisotropy. Decay of the anisotropic component corresponds either to the rotational diffusion of the molecule or to the intramolecular vibrational energy transfer among the degenerate CO stretch modes. The time constant of the anisotropy decay, tauaniso, shows distinct solvent dependence. By comparing the results for the T1u CO stretch of W(CO)6 and the A1 CO stretch of W(CO)5(CS), the time constant of the rotational diffusion, taur, and the time constant of the intramolecular energy transfer among the three degenerate vibrational modes, taue, are determined as 12 and 8 ps, respectively. The tauaniso value increases as the number of carbon atoms in the alkane solvent increases. After 10 ps, the recovery of the bleaching becomes isotropic. The isotropic decay represents the vibrational population relaxation, from v=1 to v=0. In heptane, the time constant for the isotropic decay, tau1, for W(CO)5(CS) and W(CO)6 was 140 ps. The tau1 for the two acetonitrile-substituted complexes, however, shows a smaller value of 80 ps. The vibrational energy relaxation of W(CO)5(CH3CN) and W(CO)5(CD3CN) is accelerated by the intramolecular energy redistribution from the CO ligand to the acetonitrile ligand. In the nine alkane solutions, the tau1 value of W(CO)6 ranges between 124 and 158 ps, showing the apparent V-shaped solvent dependence with its minimum in decane, while the tau1 value shows little solvent dependence for W(CO)5(CH3CN) and W(CO)5(CD3CN).     

亚稳态He(23S)、Ar(3P0.2)原子与C2H3分子传能反应

自由基CN、CH、H在燃烧化学、大气化学、天体发光、环境污染等方面占有极为重要的地位，对于这些自由基发光及形成动力学机理的探讨，无疑是重要的．近年来，人们利用亚稳态惰性原子与膨化物碰撞传能，探讨了CN（AB－＋X）的化学发光［‘一、发现亚稳态的Ar（‘几，。）原子与H     

Vibrational relaxation of O2(X3 Sigma g-, v = 9-13) by collisions with O2

Vibrationally excited O(2)(X(3) Sigmag(-)) was generated in the UV laser flash photolysis of O(3) and single vibrational level was detected via laser-induced fluorescence (LIF) in the B(3) Sigmau(-)-X(3) Sigmag(-) system. The time-resolved LIF of adjacent vibrational levels has been analyzed by the integrated-profiles method and the rate coefficients for single-quantum relaxation, O(2)(X(3)Sigmag(-), v = 9-13)+ O(2)(v = 0)--> O(2)(X(3)Sigmag(-), v - 1)+ O(2)(v = 1), have been determined. To the best of our knowledge, the rate coefficients for v = 12 and 13 are measured for the first time in the present study. The efficiency of relaxation is higher at lower vibrational levels, indicating that a small energy mismatch is suitable for the energy transfer. The vibrational level dependence of all the rate coefficients for the relaxation measured in the present study and previously reported by several groups can be rationalized by the energy gap law.     

CO(υ)高振动激发态向C2H2的振动传能研究

用时间分辨富里叶红外发射谱研究了高振动激发态ＣＯ向Ｃ２Ｈ２的传能，得到了ＣＯ（ｖ＝１－３）各振动态布居及其随时间的变化。利用微分法解出弛豫微分方程组，获得ＣＯ（ｖ＝１－３）向Ｃ２Ｈ２的传能速率常数分别为：２．０±０．１，６．０±０．２和９．４±０．８（１０＾－１３ｃｍ＾３·ｍｏｌｅｃｕｌｅ＾－１·ｓ＾－１）。传能速率随着振动量子数的增加而迅速增加。ＣＯ的振动能应向Ｃ２Ｈ２的对称伸缩模ｖ２近共振Ｖ－     

Doubly excited 2 1Delta g state of Na2

The doubly excited valence (3p+3p) 2 (1)Delta(g) state of Na(2) is experimentally observed by using optical-optical double resonance spectroscopy. A single line Ar(+) laser (a total of nine lines) was used to pump the sodium dimers from thermally populated ground state X (1)Sigma(g) (+) to the intermediate B (1)Pi(u) state. Then, a single mode Ti:sapphire laser was used to probe the doubly excited 2 (1)Delta(g) state. Violet fluorescence emitted from the highly excited states (mainly 2 (3)Pi(g) or 3 (3)Pi(g) states which are transferred from 2 (1)Delta(g) state via collision) to the a (3)Sigma(u) (+) state was monitored by a filtered photomultiplier tube (PMT). A total of 582 rovibrational levels of 2 (1)Delta(g) state were observed, identified, and assigned to the vibrational and rotational quantum numbers in the range of 0< or =v< or =28 and 11< or =J< or =99, respectively. The absolute vibrational quantum number assignment was verified by comparing the totally resolved fluorescence with the calculated Franck-Condon factors between 2 (1)Delta(g) state and B (1)Pi(u) state. Dunham coefficients and Rydberg-Klein-Rees potential curve were derived from these observed quantum levels. The primary molecular constants of Na(2) 2 (1)Delta(g) state are T(e)=32 416.759(15) cm(-1), omega(e)=124.8484(36) cm(-1), B(e)=0.119 158(3) cm(-1), and R(e)=3.508 20(5) A.     

Observation of L uncoupling in the 5 1Deltag Rydberg state of Na2

The phenomenon of electronic orbital angular momentum L uncoupled from its internuclear axis has been observed in the sodium dimer using high-resolution cw optical-optical double-resonance spectroscopy. When L uncoupling occurs, the degeneracy of Lambda doubling is removed. In our experiment, the intermediate B (1)Pi(u) state of Na(2) is excited from the thermally populated ground X (1)Sigma(g) (+) state by a single-line Ar(+) laser. Then, a single-mode dye laser is used to probe the Rydberg states from the intermediate state. The signals are detected by monitoring the UV fluorescence from the triplet gerade states back to the a (3)Sigma(u) (+) state via collision energy transfer. Under our experimental resolution, the splitting of Lambda doubling in the 5 (1)Delta(g) state of Na(2) can be measured. A total of 136 rovibronic levels with ef parities have been assigned to the 5 (1)Delta(g) state. The Lambda-splitting constants deduced from these data are q(0)=0.376(90)x10(-4) cm(-1), q(v)=0.114(6)x10(-4) cm(-1), and mu=0.76(33)x10(-8) cm(-1). In general, the Lambda splitting of the Delta states is considerably smaller than that of the Pi states. However, the first-order splitting constants q(0) and q(v) reported here are larger than those in the B (1)Pi(u) state. This is due to the L uncoupling of the Rydberg states.     

Quantum tunneling in the midrange vibrational fundamentals of tropolone

The Fourier transform infrared spectrum of tropolone(OH) vapor in the 1175-1700 cm(-1) region is reported at 0.0025 and 0.10 cm(-1) spectral resolutions. The 12 vibrational fundamentals in this region of rapidly rising vibrational state density are dominated by mixtures of the CC, CO, CCH, and COH internal coordinates. Estimates based on the measurement of sharp Q branch peaks are reported for 11 of the spectral doublet component separations DS(v) = |Delta(v) +/- Delta(0)|. Delta(0) = 0.974 cm(-1) is the known zero-point splitting, and three a(1) modes show tunneling splittings Delta(v) approximately Delta(0), four b(2) modes show splittings Delta(v) approximately 0.90Delta(0), and the remaining four modes show splittings Delta(v) falling 5-14% from Delta(0.) Significantly, the splitting for the nominal COH bending mode nu(8) (a(1)) is small, that is, 10% from Delta(0). Many of the vibrational excited states demonstrate strong anharmonic behavior, but there are only mild perturbations on the tautomerization mechanism driving Delta(0). The data suggest, especially for the higher frequency a(1) fundamentals, the onset of selective intramolecular vibrational energy redistribution processes that are fast on the time scale of the tautomerization process. These appear to delocalize and smooth out the topographical modifications of the zero-point potential energy surface that are anticipated to follow absorption of the nu(v) photon. Further, the spectra show the propensity for the Delta(v) splittings of b(2) and other complex vibrations to be damped relative to Delta(0).     

Acceleration of the reaction OH + CO → H + CO2 by vibrational excitation of OH

The collision complex formed from a vibrationally excited reactant undergoes redissociation to the reactant, intramolecular vibrational relaxation (randomization of vibrational energy), or chemical reaction to the products. If attractive interaction between the reactants is large, efficient vibrational relaxation in the complex prevents redissociation to the reactants with the initial vibrational energy, and the complex decomposes to the reactants with low vibrational energy or converts to the products. In this paper, we have studied the branching ratios between the intramolecular vibrational relaxation and chemical reaction of an adduct HO(v)-CO formed from OH(X(2)Π(i)) in different vibrational levels v = 0-4 and CO. OH(v = 0-4) generated in a gaseous mixture of O(3)/H(2)/CO/He irradiated at 266 nm was detected with laser-induced fluorescence (LIF) via the A(2)Σ(+)-X(2)Π(i) transition, and H atoms were probed by the two-photon excited LIF technique. From the kinetic analysis of the time-resolved LIF intensities of OH(v) and H, we have found that the intramolecular vibrational relaxation is mainly governed by a single quantum change, HO(v)-CO → HO(v-1)-CO, followed by redissociation to OH(v-1) and CO. With the vibrational quantum number v, chemical process from the adduct to H + CO(2) is accelerated, and vibrational relaxation is decelerated. The countertrend is elucidated by the competition between chemical reaction and vibrational relaxation in the adduct HOCO.     

Near-infrared laser spectroscopy of NiI

Laser-induced fluorescence spectrum of NiI in the near infrared region of 714-770 nm has been recorded. Seven bands belonging to three electronic transition systems were observed and analyzed: the (0,0), (1,0), and (2,0) bands of [13.3] (2)Sigma(+)-A (2)Pi(3/2) system; the (1,1) and (0,1) bands of [13.9] (2)Pi(3/2)-X (2)Delta(5/2) system; and the (0,0) and (1,0) bands of [13.9] (2)Pi(3/2)-A (2)Pi(3/2) system. Spectra of isotopic molecules confirmed the vibrational quantum number assignment of the observed bands. Least-squares fit of rotationally resolved transition lines yielded accurate molecular constants for the v=0-2 levels of the [13.3] (2)Sigma(+) state, the v=0 level of the A (2)Pi(3/2), and the v=1 level of the X (2)Delta(5/2) state. The vibrational separation, DeltaG(1/2), of the ground state was measured to be 276.674 cm(-1). With the observation of the [13.9] (2)Pi(3/2)-A (2)Pi(3/2) and [13.9] (2)Pi(3/2)-X (2)Delta(5/2) transitions, we accurately determined the energy separation between the A (2)Pi(3/2) and the X (2)Delta(5/2) to be 163.847 cm(-1). This confirms that the order of the A (2)Pi(3/2) and X (2)Delta(5/2) states in NiI is reversed when compared with other nickel monohalides.     

Reaction dynamics of Ca(4s3d 1D2)+CH4-->CaH(X 2Sigma+)+CH3: reaction pathway and energy disposal for the CaH product

The reaction pathway for Ca(4s3d 1D2)+CH4-->CaH(X 2Sigma+)+CH3 has been investigated by using a pump-probe technique in combination with potential-energy surface (PES) calculations. The nascent product distributions of CaH have been characterized with Boltzmann rotational temperatures of 1013+/-102 and 834+/-70 K for the v=0 and 1 levels, respectively, and a Boltzmann vibrational temperature of 1313+/-173 K. The rotational and vibrational energy partitions in CaH have been estimated to be 461+/-45 and 252+/-15 cm(-1), respectively. According to the PES calculations, the pathway favors an insertion mechanism. Ca(3 1D2) approaches CH4 along an attractive potential surface in a C2v (or Cs) symmetry and then the collision complex undergoes nonadiabatic transition to the reactive ground-state surface. An Arrhenius plot shows a potential-energy requirement of 2695+/-149 cm(-1), which accounts for the endothermicity of 2930 cm(-1) for the reaction scheme. The Ca-C bond distance in the transition state structure is short enough to allow for tight orbital overlap between CaH and CH3. The strong coupling between the moieties renders the energy transfer sufficient from CaH into the CH3 radical. As compared to the Ca(4 1P1) reaction, the dissociation lifetime of the intermediate complex with less excess energy is prolonged so as to cause much less vibrational energy disposal into CaH.     

Photodissociation spectroscopy of stored CH+ and CD+ ions: analysis of the b 3Sigma(-)-a 3Pi system

We have measured the photodissociation spectrum of CH(+) and CD(+) molecular ions, stored as fast (MeV) ion beams in the heavy-ion storage ring TSR. Several b (3)Sigma(-)-a (3)Pi bands were observed as strong resonances because a large fraction of the ions in the metastable a (3)Pi(v=0) state were pumped to b (3)Sigma(-) levels and predissociated via the c (3)Sigma(+) state into C(+) and H(D) fragments. From a rotational analysis of the 2-0, 3-0, and 4-0 bands in CH(+) and the 3-0 and 4-0 bands in CD(+), we derive spectroscopic constants for these levels and also revise a previous analysis of the 0-0 and 1-0 bands in CH(+). Combining all data delivers new, significantly adjusted equilibrium constants for the b (3)Sigma(-) and a (3)Pi electronic states. Apart from the spectroscopic analysis, we estimate the predissociation rates of the upper b (3)Sigma(-) vibrational levels in CH(+) and compare them to a model. For the initial rovibrational distribution of the stored metastable CH(+) molecules, the data indicate a faster vibrational cooling than derived before, and rotational cooling at a rate similar to the X (1)Sigma(+) ground state. New aspects of the spin-forbidden a (3)Pi-X (1)Sigma(+) radiative decay are discussed. Finally, we predict b (3)Sigma(-)-a (3)Pi absorption and a (3)Pi-X (1)Sigma(+) emission lines through which CH(+) in the metastable a (3)Pi(v=0) state might be detectable in astrophysical environments.