Dissociation of State-Selected NO₂⁺ Ions Studied by Threshold Photoelectron−Photoion Coincidence Techniques

Abstract

Fragmentation patterns and dissociation rates of state-selected NO 2 + ions were measured by the threshold photoelectron-photoion coincidence (TPEPICO) method in the region of 40-100 nm. Parent NO 2 + ions were detected when they were prepared in the excited states located above the first dissociation limit (D 0 0 ) 2.79 eV), correlating to NO + (X 1 Σ + ) + O( 3 P). Specially, the dissociation rate (k dis ) of NO 2 + ions in the lowest excited a ˜3B 2 state increases with increasing the quantum number of the bending vibration (n 2 ): (7.4 ( 4.9) × 10 2 , (1.32 ( 0.56) × 10 3 , (1.51 ( 0.40) × 10 4 , and (2.38 ( 0.51) × 10 4 s -1 for n 2 ) 0, 1, 2, and 3, respectively. The branching ratios of two dissociation pathways, NO + + O and O + + NO, were found to depend on the electronic state of the parent ion. The unimolecular dissociation channels are discussed in terms of dissociation potential surfaces open for individual electronic states and radiative relaxation to lower electronic states.

A Theoretical Study on the Electronic States and O‐Loss Photodissociation of the NO2+ Ion

“…We consider that the observed dissociation is just an A' PEC shown in Figure 2, although there is a low barrier (0.42 eV) along the PEC. The intersystem crossing mechanism was proposed for the a 3 B 2 dissociation by Shibuya et al [5] We could tell that the X 1 S g + state does not dissociate (see the last paragraph). Avoided crossing between two 3 B 2 states was considered by Eland.…”

“…Our calculations support the experimental fact that dissociation from the ground X 1 S + state was not observed. [12] Shibuya et al [5] and Eland and Karlsson [12] observed dissociation from vibration levels of the a 3 B 2 state to the first dissociation limit. We consider that the observed dissociation is just an A' PEC shown in Figure 2, although there is a low barrier (0.42 eV) along the PEC.…”

“…In their threshold photoionization spectrum of NO 2 , Jarvis et al [19] [4][5][6][7][8][9][10][11][12][13][14][15][16] The researchers detected many dissociation products, thus indicating many dissociation channels, and they were also interested in the branching ratios of different dissociation channels and the dissociation rates in different states of NO 2 + . Herein, we study only O-loss photodissociation in low-lying states of NO 2 + (we will not study branching ratios of dissociation and dissociation rates).…”

Molecular frame and recoil frame photoelectron angular distributions from dissociative photoionization of NO2

“…[24][25][26][27] The lifetimes of several of the excited ion states have been studied: 25 the ͑4b 2 ͒ −1 a 3 B 2 and ͑1a 2 ͒ −1 A 1 A 2 states were found to be metastable with lifetimes on the order of microseconds, whereas the ͑1a 2 ͒ −1 b 3 A 2 state was found to dissociate rapidly with a lifetime on the order of 10 −13 s. Higher lying ion states were also found to have short lifetimes. 22 and 23͒ and the corresponding dissociative photoionization cross sections.…”

Charged and Neutral NO3 Isomers from the Ionization of NOx and O3 Mixtures

“…[19] Thus the singlet and the triplet surfaces of Figure 10 are characterized by different geometries of the species involved: species with a linear nitro group, namely the NO 5 ion 1, the NO 4 ion 4, and the NO 3 ion 13 are located on the singlet surface; species with a bent nitro group, namely the NO 5 ion 2, the NO 4 ion 5, and the NO 3 ions 8 and 9, are located on the triplet surface.…”