<i>Ab initio</i> potential energy surfaces, total absorption cross sections, and product quantum state distributions for the low-lying electronic states of N2O

The energy partitioning in the UV photodissociation of N 2 O is investigated by means of quantum mechanical wave packet and classical trajectory calculations using recently calculated potential energy surfaces. Vibrational excitation of N 2 is weak at the onset of the absorption spectrum, but becomes stronger with increasing photon energy. Since the NNO equilibrium angles in the ground and the excited state differ by about 70• , the molecule experiences an extraordinarily large torque during fragmentation producing N 2 in very high rotational states. The vibrational and rotational distributions obtained from the quantum mechanical and the classical calculations agree remarkably well. The shape of the rotational distributions is semi-quantitatively explained by a two-dimensional version of the reflection principle. The calculated rotational distribution for excitation with λ = 204 nm and the translational energy distribution for 193 nm agree well with experimental results, except for the tails of the experimental distributions corresponding to excitation of the highest rotational states. Inclusion of nonadiabatic transitions from the excited to the ground electronic state at relatively large N 2 -O separations, studied by trajectory surface hopping, improves the agreement at high j.

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confidence: 99%

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confidence: 99%

Photodissociation of N2O: Energy partitioning

Schmidt

Lorenz²,

McBane

et al. 2011

“…Recent calculations predict that over 97% of the absorption at 204 nm involves excitation to the 2 1 A' state, i.e., a parallel transition, which means the dipole moment lies in the plane of the molecule. 23,25,26,28,31 This of course means the β values can vary dramatically depending on the direction of the transition dipole moment with respect to the N-O bond direction. Interpretations of the deviation of β from the limiting value invoked a non-axial recoil mechanism, especially as the KER becomes small.…”

Section: Analysis and Discussionmentioning

confidence: 99%

“…In recent years N 2 O has been subject to a number of high resolution experiments [13][14][15][16] using VMI, [17][18][19][20][21][22] as well as high level theoretical calculations. [23][24][25][26][27][28][29][30][31][32] In the most recent VMI study of Suzuki and coworkers, 22 the authors ionized individual rotational states of the N 2 photoproduct. Velocity map images showed three distinct velocities, corresponding to photodissociation of the three lowest vibrational states (0, v 2 ≤ 2, 0) of N 2 O, which were populated in the molecular beam expansion.…”

Section: Introductionmentioning

confidence: 99%

Single-field slice-imaging with a movable repeller: Photodissociation of N2O from a hot nozzle

Harding

Neugebohren

Grütter

et al. 2014

Laser initiated reactions in N2O clusters studied by time-sliced ion velocity imaging technique J. Chem. Phys. 139, 044307 (2013) We present a new photo-fragment imaging spectrometer, which employs a movable repeller in a single field imaging geometry. This innovation offers two principal advantages. First, the optimal fields for velocity mapping can easily be achieved even using a large molecular beam diameter (5 mm); the velocity resolution (better than 1%) is sufficient to easily resolve photo-electron recoil in (2 + 1) resonant enhanced multiphoton ionization of N 2 photoproducts from N 2 O or from molecular beam cooled N 2 . Second, rapid changes between spatial imaging, velocity mapping, and slice imaging are straightforward. We demonstrate this technique's utility in a re-investigation of the photodissociation of N 2 O. Using a hot nozzle, we observe slice images that strongly depend on nozzle temperature. Our data indicate that in our hot nozzle expansion, only pure bending vibrations -(0, v 2 , 0) -are populated, as vibrational excitation in pure stretching or bend-stretch combination modes are quenched via collisional near-resonant V-V energy transfer to the nearly degenerate bending states. We derive vibrationally state resolved absolute absorption cross-sections for (0, v 2 ≤ 7, 0). These results agree well with previous work at lower values of v 2 , both experimental and theoretical. The dissociation energy of N 2 O with respect to the O( 1 D) + N 2 1 + g asymptote was determined to be 3.65 ± 0.02 eV.

“…Hopper 1 published an influential theoretical study of the electronic structure of N 2 O, and several later treatments have provided more detail. [2][3][4][5] The first absorption band could have contributions from two different singlet electronic states in linear N 2 O, the first 1 1 A excited states are both strongly bent and consequently the N 2 product is rotationally excited. The transition dipole moment calculations of both Daud et al 3 and Nanbu and Johnson 4 indicate that absorption to 2 1 A should be stronger than that to 1 1 A .…”

Section: Introductionmentioning

confidence: 99%

Product angular distributions in the ultraviolet photodissociation of N2O

McBane

Schinke

2012

The angular distribution of products from the ultraviolet photodissociation of nitrous oxide yielding O( 1 D) and N 2 (X 1 + g ) was investigated using classical trajectory calculations. The calculations modeled absorption only to the 2 1 A electronic state but used surface-hopping techniques to model nonadiabatic transitions to the ground electronic state late in the dissociation. Observed values of the anisotropy parameter β, which decrease as the product N 2 rotational quantum number j increases, could be well reproduced. The relatively low observed β values arise principally from nonaxial recoil due to the very strong bending forces present in the excited state. In the main part of the product rotational distribution near 203 nm, an unusual dynamical effect produces the decrease in β with increasing j; nonaxial recoil effects remain approximately constant while higher j product molecules arise from parent molecules that had their transition dipole moments aligned more closely along the molecular axis. In both low and high j tails of the rotational distribution, the variations in β with j are caused by changes in the extent of nonaxial recoil. In the high-j tail, additional torque present on the ground state potential energy surface following nonadiabatic transitions causes both the additional rotational excitation and the lower β values.