No abstract

Collision-induced rotational alignment of NO X 2 ⌸ 1/2 (vϭ0,jϭ8.5) is measured for rotationally inelastic scattering of NO X 2 ⌸ 1/2 (vϭ0,jϭ0.5) with Ar at 65 meV collision energy. The experiments are performed by velocity-mapped ion imaging with polarized 1ϩ1Ј REMPI probing of the scattered NO products. It is shown that the azimuthal information intrinsic to imaging detection allows the measurement of additional alignment moments not previously reported. The measured alignment shows only qualitative agreement with the predictions of the kinematic apse conservation model.

The binding energy of the NO dimer has been measured directly using velocity-mapped ion imaging. NO dimer is photodissociated to produce NO(X) and NO(A), and the NO(A) is then nonresonantly ionized to NO+. The threshold for production of NO+ ions is measured at 44 893±2 cm−1, which corresponds to a binding energy of 696±4 cm−1.

The rotational energy release in the dissociation of ketene along its singlet potential energy surface is observed and compared with various statistical and dynamical theories. Rotational distributions for CO(X̃ 1Σ+)(v=1) are measured from the threshold for production of CH2(ã 1A1)(0,0,0) + CO(X̃ 1Σ+)(v=1) to 1720 cm-1 above. At low energies (≤200 cm-1), phase space theory (PST) matches the observed distributions. At 357 and 490 cm-1, PST, constrained by the measured state distributions of the methylene fragment, provides a good fit. For E ≥ 1107 cm-1, the constrained PST matches the average rotational energy observed but gives distributions which are broader than observed. This contrasts with the 1CH2 fragment rotations which become progressively colder than PST as energy increases from 200 cm-1 above the threshold. The CO(v=1) rotational distributions for E ≥ 357 cm-1 contain no measurable product from triplet channel fragmentation. They can be compared with the previously determined CO(v=0) rotational distributions in order to partition the yield between singlet and triplet channels and recalculate the singlet yield. This yield is found to be at the upper limit of the range previously reported.

We have investigated the dissociation dynamics of the ArNO van der Waals molecule near 225 nm. This photon energy excites ArNO as much as 400 cm -1 above the photodissociation threshold, producing Ar + NO(A 2 Σ + ,V)0,N)0-12). In the first series of experiments, we deduce the population of rotational levels produced in NO(A) during photodissociation of ArNO with resonance enhanced multiphoton spectroscopy (REMPI) through the E-state. The rotational state distributions show anomalous nonstatistical behavior peaking near high N states. This behavior is consistent with the rotational rainbow effects observed by others with the maximum rotational quantum number proportional to the square root of the available energy. In the second experiments, 225 nm photons sequentially dissociate ArNO and then nonresonantly ionize the NO(A) products, which we observe using velocity-mapped ion imaging. The ion images display rings corresponding to the production of different rotational states of NO(A) during dissociation. We measure the appearance threshold for products from dissociation of ArNO to produce NO(A,N)0) as 44291 ( 2 cm -1 . Finally, we observe the contribution of hot bands to the rotational state distribution.