Yo Fujimura

Energy partitioning in two kinds of NO molecules generated from the reaction of O(1D) with N2O: Vibrational state distributions of “new” and “old” NO’s

The reaction of O(1D) with N2O produces two kinds of NO molecules, the “old” one which originally exists in N2O and the “new” one which includes the attacking O atom. Using the isotopically labeled reagent, we determined the vibrational state distributions of these NO’s (X 2Π; v=0–17) separately. To obtain the distributions, two types of experiments were performed with the laser-induced fluorescence (LIF) technique via the NO A←X and B←X transitions. First, the relative populations of NO molecules (the sum of the two kinds of NO’s) in v=0–11 levels were measured with unlabeled reagents. Then, isotopically labeled reaction, 18O(1D)+N216O→N18O+N16O, was utilized to determine the relative ratio between the two kinds of NO’s in the vibrational levels of v=0–5 and 12–15. Combining the above results with previously determined vibrational state distribution of NO in high vibrational levels (v=11–17) [J. Chem. Soc., Faraday Trans. 94, 1575 (1998)], we were able to obtain a complete set of vibrational state distri...

Photodissociation of the NO dimer: rotational energy distribution and alignment of the NO(B 2Π) fragments

Abstract We have determined the rotational distribution and the rotational alignment A (2) 0 of the photofragment NO (B 2 Π; v =0) produced on the photodissociation of the NO dimer at 193 nm. The rotational spectrum observed can be reproduced under the assumption of a bimodal distribution with dual rotational temperatures, 400 and 1400 K. This Boltzmann-like distribution indicates the occurrence of energy randomization among the low-frequency van der Waals modes, in spite of the dissociation along the repulsive energy surface. The observed negative value of the rotational alignment A (2) 0 , around −0.1, implies that the NO dimer preferentially dissociates via a planar geometry. The excitation of the out-of-plane motion due to the energy randomization may offer an explanation for the deviation of A (2) 0 from the limiting value −0.4 (complete planarity).

Stereodynamics of the reactions of O(3P) with saturated hydrocarbons: The dependences on the collision energy and the structural features of hydrocarbons

State-selected differential cross sections (DCSs) have been measured for the OH radicals produced from the reactions of O(3P) with saturated hydrocarbons by utilizing Doppler-resolved polarization spectroscopy. Stereodynamics in the reactions of secondary (c-C6H12) and tertiary (i-C4H10) hydrogen atoms are discussed based on the dependences of the DCSs on the collision energy and the structure of these hydrocarbons. For the c-C6H12 reaction, the DCS of the OH(2Π3/2,v′=1,j′=3.5,A′) shows predominant intensities in the backward hemisphere with reference to the incident O(3P) atom at a mean collision energy of 〈Ecoll〉=12 kJ/mol. When the collision energy is raised to 〈Ecoll〉=33 kJ/mol, the OH radicals scattered in the forward hemisphere grow almost to match those in the backward hemisphere. The observed increase in the forward scattering implies that the collision energy makes the large impact parameter collisions contribute to the reactive scattering. At a similar collision energy of 〈Ecoll〉=31 kJ/mol the f...

Scalar and vector properties of the NO(v′=0) produced from the reaction O(1D)+N2O→NO+NO

We have measured the product state-selected differential cross-section (DCS), and the rotational angular momentum polarization, together with the energy distributions for the reaction O(1D)+N2O→NO+NO by utilizing Doppler-resolved polarization spectroscopy. The reaction dynamics of the vibrational channel forming the product NO(v′=0) is discussed based on both the scalar and vector properties. The product rotational and center-of-mass translational energy distributions are described as Boltzmann distributions with Trot≈10 000 K and Ttr≈13 000 K, respectively. These energy distributions are close to statistical predictions. The product DCS has substantial intensities over the whole angular range with a slight preference for backward scattering. The product rotational angular momentum vector j′ does not have a noticeable angular correlation with either k or k′ (the relative velocity vectors of the reactant and product, respectively). This nearly isotropic angular distribution of j′ indicates that both in-pla...

Theoretical investigation of the potential energy surfaces for the O(1D)+N2O reaction

Abstract Potential energy surfaces for the O( 1 D )+N 2 O reaction have been calculated using multiconfiguratonal second-order perturbation theory (CASPT2) with Dunnings correlation-consistent polarized valence double-zeta basis set. It has been found that a wide range of the O( 1 D )–N–N approach angles from collinear to nearly perpendicular configurations is attractive on the lowest 1 A ′ surface. The calculations show that the height of the exit barrier for the NO+NO production is strongly dependent on the O( 1 D )–N–N angle. This suggests that the dynamics of the NO+NO channel is significantly affected by both the initial approach and subsequent bending motion of the O( 1 D )–N–N angle. The reaction mechanism for the O 2 +N 2 production channel is also discussed.

Vibrational state distribution of highly vibrationally excited NO(X 2Π) generated from the reaction of O(1D) with N2O

The vibrational state distribution has been determined for vibrationally excited NO(X 2Π; v = 11–17) produced by the reaction of O(1D) with N2O. O(1D) atoms were generated by O3 photodissociation at 266 nm and the laser-induced fluorescence (LIF) technique via the NO B 2Π←X 2Π transition was utilized to obtain the vibrational state distribution. The LIF spectra were taken under conditions in which the vibrational relaxation of NO is negligible while its rotational relaxation is sufficiently achieved. The rate constant for quenching by O3 was also determined, as the loss of NO(B) due to quenching by reactant gases should be taken into account when the LIF data are analysed. Based on the large exothermicity of this reaction, significant excitation in the vibrational state of NO(X) is expected; however, the vibrational state distribution was similar to, but slightly colder than, that predicted from statistical theories. Possible mechanisms which may explain such an unexpected distribution are discussed.

9,9′-Bianthryl and its van der Waals complexes studied by rotational coherence spectroscopy: Structure and excited state dynamics

The structure and excited state dynamics of jet-cooled 9,9′-bianthryl (BA) and its 1:1 van der Waals (vdW) complexes with Ne, Ar, and H2O were studied using rotational coherence spectroscopy (RCS). For a free BA molecule, the magnitude and persistence of the recurrent transient appearing in the time-correlated single photon counting (TCSPC) measurement was found to be dependent on the torsional level of BA, indicating the rotational constant changes with the torsional energy level. The RCS–TCSPC measurement of the BA–Ar and BA–H2O complexes in the S1 state showed no coherent transients. However, the pump–probe time-resolved fluorescence depletion (TRFD) detected the weak J-type transient. Those facts imply the loss of coherence in the BA vdW complexes due to the excited-state dynamics, which coincides with the analysis of the laser-induced fluorescence excitation and dispersed fluorescence spectra. The structure of the ground-state 1:1 BA complex with Ne, Ar, and H2O was determined based on the RCS transi...

Stereodynamics of the vibrational channel O(1D)+H2O→OH(v′=2)+OH

The state-selected differential cross section (DCS) and rotational angular momentum polarization for the reaction O(1D)+H2O→OH+OH have been measured by utilizing the polarized Doppler-resolved laser-induced fluorescence probing technique. Stereodynamics of the reaction channel forming the newly formed OH in the specific vibrational level v′=2 is discussed on the basis of the vector properties. A nearly isotropic DCS for the product OH(2Π3/2, v′=2, j′=5.5) most probably indicates that the reaction is dominated by an insertion mechanism involving a collisional HOOH complex with a lifetime comparable to its rotational period. The extremely asymmetrical energy partitioning between the two OH fragments, therefore, suggests that the redistribution of the available energy does not occur on a time scale comparable to the rotational period of the complex. Furthermore, it has been found that the product rotational angular momentum vector j′ is predominantly perpendicular to the collision plane spanned by k and k′ (...

Nascent state distributions of NO(X 2Π) generated from the reaction of S(1D) with N2O: Intramolecular vibrational-energy redistribution in the reaction intermediate

The nascent internal state distribution of NO(X 2Π) generated from the reaction, S(1D)+N2O→NO+NS, has been determined by utilizing the laser-induced fluorescence (LIF) technique. The average vibrational energy of NO relative to the statistically expected value is found to be 37%. This amount is obviously smaller than that of the fragment N 16O of the isovalent reaction 18O(1D)+N2 16O→N 18O+N 16O, though it is still larger than that of 18OH produced from the 16O(1D)+H2 18O reaction. To interpret the observed difference in the product energy partitioning, we have applied the quantal intramolecular vibrational-energy redistribution (IVR) representation to the energy mixing in the collision complex. Using a local-mode vibration model with momentum couplings, we have extracted the crucial factors determining the energy partitioning in these reactions. The reaction system consisting of only heavy mass atoms generally has a large vibrational coupling and a large density of states, both of which favor the rapid e...

Rotational coherence spectroscopy of 9,9′-bianthyrl and its van der Waals complexes with Ar and H2O

Abstract The excited state structure and dynamics of 9,9′-bianthryl and its Ar/H 2 O complexes have been studied using rotational coherence spectroscopy (RCS). The intensity and the decay of the RCS signal were found to be dependent on the torsional level of the bianthryl, reflecting the change of rotational constants with torsional levels. For the Ar and H 2 O complexes, no RCS signals were observed in a time-correlated single photon counting (TCSPC) experiment, though small signals were detected by a pump-probe time-resolved fluorescence depletion measurement. The smallness of the signal for the Ar complex is mostly attributed to structural reasons — deviation from a symmetric top and a hybrid-type transition unfavorable to RCS signals. For the H 2 O complex, the loss of coherence due to the rapid conversion of the electronic state is responsible for the absence of the signal in the TCSPC measurements.