Energy transfer to CO(v) in the O(1D)+CO(1Σ+g) reaction

Topology of conical/surface intersections among five low-lying electronic states of CO2: multireference configuration interaction calculations

Multi-reference configuration interaction with single and double excitation method has been utilized to calculate the potential energy surfaces of the five low-lying electronic states (1)A1, (1)A2, (3)A2, (1)B2, and (3)B2 of carbon dioxide molecule. Topology of intersections among these five states has been fully analyzed and is associated with double-well potential energy structure for every electronic state. The analytical potential energy surfaces based on the reproducing kernel Hilbert space method have been utilized for illustrating topology of surface crossings. Double surface seam lines between (1)A1 and (3)B2 states have been found inside which the (3)B2 state is always lower in potential energy than the (1)A1 state, and thus it leads to an angle bias collision dynamics. Several conical∕surface intersections among these five low-lying states have been found to enrich dissociation pathways, and predissociation can even prefer bent-geometry channels. Especially, the dissociation of O((3)P) + CO can take place through the intersection between (3)B2 and (1)B2 states, and the intersection between (3)A2 and (1)B2 states.

Anomalous enrichment of 17O and 13C in photodissociation products of CO2: possible role of nuclear spin

Oxygen and carbon isotope fractionation associated with products (CO and O(2)) of gas phase photodissociation of CO(2) have been studied using photons from Hg lamp (184.9 nm) and Kr lamp (123.6 and 116.5 nm). In dissociation by Hg lamp photons both CO and O(2) are enriched in (17)O by about 81 per thousand compared to the estimate based on a kinetic model. Additionally, CO is enriched in (13)C by about 37 per thousand relative to the model composition. In contrast, in dissociation by higher energy Kr lamp photons no such anomaly was found in O(2). The observed isotopic enrichments in case of Hg lamp dissociation are proposed to be due to a hyperfine interaction between nuclear spin and electron spins or orbital motion causing enhanced dissociation of isotopologues of CO(2) containing (17)O and (13)C. The (17)O enrichment is higher than that of (13)C by a factor of 2.2+/-0.2 which can be explained by the known magnetic moment ratio of (17)O and (13)C due to differing nuclear spins and g-factors. These results have potential implications in studies of the planetary atmospheres.

Distribution of Internal States of CO from O (1D) + CO Determined with Time-Resolved Fourier Transform Spectroscopy

Following collisions of O (1D) with CO, rotationally resolved emission spectra of CO (1 < or = v < or = 6) in the spectral region 1800-2350 cm(-1) were detected with a step-scan Fourier transform spectrometer. O (1D) was produced by photolysis of O3 with light from a KrF excimer laser at 248 nm. Upon irradiation of a flowing mixture of O3 (0.016 Torr) and CO (0.058 Torr), emission of CO (v < or = 6) increases with time, reaches a maximum approximately 10 micros. At the earliest applicable period (2-3 micros), the rotational distribution of CO is not Boltzmann; it may be approximately described with a bimodal distribution corresponding to temperatures approximately 8000 and approximately 500 K, with the proportion of these two components varying with the vibrational level. A short extrapolation from data in the period 2-6 micros leads to a nascent rotational temperature of approximately 10170 +/- 600 K for v = 1 and approximately 1400 +/- 40 K for v = 6, with an average rotational energy of 33 +/- 6 kJ mol(-1). Absorption by CO (v = 0) in the system interfered with population of low J levels of CO (v = 1). The observed vibrational distribution of (v = 2):(v = 3):(v = 4):(v = 5):(v = 6) = 1.00:0.64:0.51:0.32:0.16 corresponds to a vibrational temperature of 6850 +/- 750 K. An average vibrational energy of 40 +/- 4 kJ mol(-1) is derived based on the observed population of CO (2 < or = v < or = 6) and estimates of the population of CO (v = 0, 1, and 7) by extrapolation. The observed rotational distributions of CO (1 < or = v < or = 3) are consistent with results of previous experiments and trajectory calculations; data for CO (4 < or = v < or = 6) are new.

Photodetachment and photofragmentation pathways in the [(CO2)2(H2O)m]− cluster anions

The mass-selected [(CO(2))(2)(H(2)O)(m)](-) cluster anions are studied using a combination of photoelectron imaging and photofragment mass spectroscopy at 355 nm. Photoelectron imaging studies are carried out on the mass-selected parent cluster anions in the m=2-6 size range; photofragmentation results are presented for m=3-11. While the photoelectron images suggest possible coexistence of the CO(2) (-)(H(2)O)(m)CO(2) and (O(2)CCO(2))(-)(H(2)O)(m) parent cluster structures, particularly for m=2 and 3, only the CO(2) (-) based clusters are both required and sufficient to explain all fragmentation pathways for m>/=3. Three types of anionic photofragments are observed: CO(2) (-)(H(2)O)(k), O(-)(H(2)O)(k), and CO(3) (-)(H(2)O)(k), k</=m, with their yields varying depending on the parent cluster size. Of these, only CO(2) (-)(H(2)O)(k) can potentially result from (O(2)CCO(2))(-)(H(2)O)(m) parent structures, although an alternative mechanism, involving the dissociation and recombination of the CO(2) (-) cluster core, is possible as well. The O(-)(H(2)O)(k) and CO(3) (-)(H(2)O)(k) channels are believed to be triggered by the dissociation of the CO(2) (-) cluster core. In the CO(3) (-)(H(2)O)(k) channel, seen only in the range of m=3-6, the CO(2) (-) core dissociation is followed by an intracluster association of nascent O(-) with the solvent CO(2). This channel's absence in larger clusters (m>6) is attributed to hindrance from the H(2)O molecules.

Collision-induced desorption in 193-nm photoinduced reactions in (O2+CO) adlayers on Pt(112)

The spatial distribution of desorbing O(2) and CO(2) was examined in 193-nm photoinduced reactions in O(2)+CO adlayers on stepped Pt (112)=[(s)3(111)x(001)]. The O(2) desorption collimated in inclined ways in the plane along the surface trough, confirming the hot-atom collision mechanism. In the presence of CO(a), the product CO(2) desorption also collimated in an inclined way, whereas the inclined O(2) desorption was suppressed. The inclined O(2) and CO(2) desorption is explained by a common collision-induced desorption model. At high O(2) coverage, the CO(2) desorption collimated closely along the (111) terrace normal.