Photoelectron Imaging Study of the Effect of Monohydration on O₂^- Photodetachment

Abstract

The photodetachment of the O(2)(-).H(2)O cluster anion at 780 and 390 nm is investigated in comparison with O(2)(-) using photoelectron imaging spectroscopy. Despite the pronounced shift in the photoelectron spectra, the monohydration has little effect on the photoelectron angular distributions: for a given wavelength and electron kinetic energy (eKE) range, the O(2)(-).H(2)O angular distributions are quantitatively similar to those for bare O(2)(-). This observation confirms that the excess electron in O(2)(-).H(2)O retains the overall character of the 2ppi(g) HOMO of O(2)(-). The presence of H(2)O does not affect significantly the partial wave composition of the photodetached electrons at a given eKE. An exception is observed for slow electrons, where O(2)(-).H(2)O exhibits a faster rise in the photodetachment signal with increasing eKE, as compared to O(2)(-). The possible causes of this anomaly are (i) the long-range charge-dipole interaction between the departing electron and the neutral O(2).H(2)O skeleton affecting the slow-electron dynamics; and (ii) the s wave contributions to the photodetachment, which are dipole-forbidden for pi(g)(-1) transitions in O(2)(-), but formally allowed in O(2)(-).H(2)O due to lower symmetry of the cluster anion and the corresponding HOMO.

Vibronic coupling in the superoxide anion: The vibrational dependence of the photoelectron angular distribution

“…The anisotropy parameter is extracted by plotting I͑E , ͒ against P 2 ͑cos ͒ at a given E. We note that the ␤ values reported in this work differ slightly from those previously reported. 28,35 This is not too surprising, considering that ␤ values are very sensitive to image distortion ͑imparted by external fields or imperfect focusing͒ and detector saturation. In the present work, extreme care has been applied to minimize such adverse effects.…”

“…at detachment wavelengths 780 nm ͑open circles͒, 396 nm ͑closed circles͒, 35 and 488 nm ͑open squares͒. 28 ␤ characterizes the PAD, and a change is clearly seen in the 780 nm data.…”

“…1 Several detachment studies of this species have probed the photon energy dependence of the total detachment cross section [19][20][21][22][23][24][25][26] or reported the photoelectron spectrum of O 2 − . 1,[27][28][29][30][31][32][33][34][35][36][37][38] Until very recently, much less data were reported regarding the PAD. 1,28,35 Among other anions, the prominent dependence of photoelectron anisotropy on the final vibrational state of the neutral was reported in the photodetachment of NO − .…”

“…1,[27][28][29][30][31][32][33][34][35][36][37][38] Until very recently, much less data were reported regarding the PAD. 1,28,35 Among other anions, the prominent dependence of photoelectron anisotropy on the final vibrational state of the neutral was reported in the photodetachment of NO − . 39 In the case of neutral diatomic molecules, dramatic changes in the PAD have been observed between different vibronic photoionization bands of N 2 , CO, and O 2 .…”

Communication: Photoelectron angular distributions of CH− reveal a temporary anion state

“…[1][2][3][4][5][6][7][8][9][10] In addition to measuring traditional photoelectron spectra, the imaging experiment also provides an extra set of information, the photoelectron angular distributions (PADs). The PAD carries information about the parent ion orbital from which the electron is detached.…”