Isotope effects in H+(D+) desorption induced by 4a1← O 1s resonant transition of condensed H2O (D2O)

Construction and Evaluation of a Miniature Electron Ion Coincidence Analyzer Mounted on a Conflat Flange with an Outer Diameter of 114 mm

“…Recently, we have developed an analyzer that can be used for both EICO analysis and APECS. 8 EICO spectroscopy has been widely applied in studies of ion desorption from condensed molecules on surfaces such as H2O, 13,[15][16][17][18] NH3, 19 CH3CN, 20 C6H6, 21 Si(CH3)4, 22 SiF3CH2CH2Si(CH3)3, 23 CH3CF3, 24 and N2O, 25 We have developed a miniature electron ion coincidence (EICO) analyzer mounted on a conflat flange with an outer diameter of 114 mm. It consists of a cylindrical mirror analyzer (CMA), a time-of-flight ion mass spectrometer (TOF-MS), a commercially available linear motion feedthrough, and a tilt adjustment mechanism.…”

“…These AEY and TIY results agree with those reported in previous studies. 13,[15][16][17][18] Auger-electron photoion coincidence (AEPICO) spectrum Figure 6 shows an Auger-electron photoion coincidence timeof-flight (AEPICO TOF) spectrum of H2O condensed on Si(111) at hv = 532.9 eV corresponding to the 4a1 ← O 1s resonance. The AEPICO TOF spectrum was measured using the EICO analyzer with a multichannel scaler triggered by the electron signal detected with the CMA at an Auger-electron kinetic energy (AeKE) of 516.5 eV (Fig.…”

“…8): (1) a surface H2O molecule is excited into the (1s) -1 (4a1) 1 state by absorbing a photon at hv = 532.9 eV; (2) HO-H bond is extended within the lifetime of (1s) -1 (4a1) 1 state (about ∼4.3 fs) 46 due to the antibonding character of the 4a1 orbital (ultrafast O-H extension); (3) the H2O with extended O-H bond is relaxed into a (valence orbitals) -2 (4a1) 1 state emitting a spectator Auger electron (this process is named as a spectator Auger transition, because the excited electron does not participate in the Auger process); and (4) the H + ion is desorbed along the repulsive potential energy surface of the (valence orbitals) -2 (4a1) 1 state. 13,[15][16][17][18] The enhancement of the H + yield at the 4a1 ← O 1s resonance (Fig. 5) was attributed to the ultrafast O-H extension in the second step.…”

“…5) was attributed to the ultrafast O-H extension in the second step. 13,[15][16][17][18] The desorption probability of the H + ion is much enhanced, because the H atom in the extended O-H get away from the surface and acquires a kinetic energy in the second step (Fig. 8).…”

“…The main component of the AES is normal O KVV Auger electrons from H2O in the bulk, 15,16 while the H + AEPICO spectrum predominantly reflects the spectator Auger process of surface H2O. 13,[15][16][17][18] Thus the above four-step mechanism can explain why the position of the AEPICO peak is shifted by about 5 -10 eV to the higher-AeKE side than that of the AES.…”