Photodissociation of N2O: Temperature dependence

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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.

supporting

confidence: 75%

Photodissociation of N2O: Energy partitioning

Schmidt

Lorenz²,

McBane

et al. 2011

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“…We have studied the photodissociation of N 2 O in a series of papers and essentially all experimental results have been well reproduced. [41][42][43][44][45][46][47][48][49] A consistent and nearly complete picture has thus been obtained. This paper is part of a similar investigation of the UV photodissociation of OCS.…”

Section: Introductionmentioning

confidence: 56%

The ultraviolet spectrum of OCS from first principles: Electronic transitions, vibrational structure and temperature dependence

Schmidt

Johnson

McBane

et al. 2012

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Global three dimensional potential energy surfaces and transition dipole moment functions are calculated for the lowest singlet and triplet states of carbonyl sulfide at the multireference configuration interaction level of theory. The first ultraviolet absorption band is then studied by means of quantum mechanical wave packet propagation. Excitation of the repulsive 2 1 A state gives the main contribution to the cross section. Excitation of the repulsive 1 1 A state is about a factor of 20 weaker at the absorption peak (E ph ≈ 45 000 cm −1 ) but becomes comparable to the 2 1 A state absorption with decreasing energy (35 000 cm −1 ) and eventually exceeds it. Direct excitation of the repulsive triplet states is negligible except at photon energies E ph < 38 000 cm −1 . The main structure observed in the cross section is caused by excitation of the bound 2 3 A state, which is nearly degenerate with the 2 1 A state in the Franck-Condon region. The structure observed in the low energy tail of the spectrum is caused by excitation of quasi-bound bending vibrational states of the 2 1 A and 1 1 A electronic states. The absorption cross sections agree well with experimental data and the temperature dependence of the cross section is well reproduced.

“…Schinke and co-workers have extensively studied the photoexcitation of the molecule in this region and indicate that the absorption cross section increases dramatically as the amount of bending excitation increases. [27][28][29][30][31][32] This explains why for a beam of cooled N 2 O, even a small population in bending excited states can be seen by photodissociation. Experimental relative absorption cross sections σ (ν 2 ) for v 2 = 0, 1, 2 have been reported by Suzuki and co-workers 22 , while Schinke 29, 32 and co-workers have calculated absolute values for σ ( ν 2 ) up to…”

Section: Analysis and Discussionmentioning

confidence: 97%

“…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.