Vacuum Ultraviolet Negative Photoion Spectroscopy of Chloroform

Abstract

Negative ions Cl(-), Cl(2)(-), CCl(-), CHCl(-), and CCl(2)(-) are observed in vacuum-ultraviolet ion-pair photodissociations of chloroform (CCl(3)H) using the Hefei synchrotron radiation facility, and their ion production efficiency curves are recorded in the photon energy range of 10.00-21.50 eV. Two similar spectra of the isotope anions (35)Cl(-) and (37)Cl(-) indicate the following: Besides the strong bands corresponding to the electron transitions from valence to Rydberg orbitals converging to the ionic states, some additional peaks can be assigned with the energetically accessible multibody fragmentations; a distinct peak at photon energy 14.55 eV may be due to a cascade process (namely, the Cl(2) neutral fragment at the highly excited state D'2(3)Π(g) may be produced in the photodissociation of CCl(3)H, and then the Cl(-) anions are produced in the pulsed-field induced ion-pair dissociations of Cl(2) (D'2(3)Π(g))); two vibrational excitation progressions, nν(2)(+) and nν(2)(+) + ν(3)(+), and nν(4)(+) and nν(4)(+) + ν(2)(+), are observed around C̃ (2)E and D̃ (2)E ionic states, respectively. The enthalpies of the multibody fragmentations to Cl(2)(-), CCl(-), CHCl(-), and CCl(2)(-) are calculated with the thermochemistry data available in the literature, and these multibody ion-pair dissociation pathways are tentatively assigned in the respective anion production spectra.

Positive and Negative Photoion Spectroscopy Study of Monochlorothiophenes

“…If these valence-to-Rydberg state transitions couple with the ion-pair dissociation paths, the resonant peaks can be observed in the IPAES. ,− However, as shown in Figure , such resonant coupling may be quite weak at the higher photon energies. On the other hand, the multibody fragmentations formulated in eq may be predominant in the higher energy range. , According to the thermodynamic values in Table and using eq , the thresholds of Cl – can be deduced as: 2 - normalC 4 normalH 3 SCl + h normalν → 2 - normalC 4 normalH 3 normalS + + Cl − false( theoretical : 9.50 nobreak.25em eV ; experimental : 8.19 nobreak.25em eV ± 0.04 nobreak.25em eV false) 3 - normalC 4 normalH 3 SCl + h normalν → 3 - normalC 4 normalH 3 normalS + + Cl − false( theoretical : 9.14 nobreak.25em eV ; experimental : 8.19 nobreak.25em eV ± 0.04 nobreak.25em eV false) These two thresholds cannot be directly determined in the present IPAES because of the much low Cl – signals at the lower photon energies. Above large deviations between the theoretical thresholds and the experimental values may also be due to the ring-opening mechanism of C 4 H 3 S + as mentioned before.…”

“…The production efficiency spectra of the positive and negative photoions were measured at the atomic and molecular physics end-station of the National Synchrotron Radiation Facility at Hefei, China. The apparatus used in the present ion-pair photodissociation study was described previously in detail. − Briefly, the VUV photon beam was monochromatized with the undulator-based spherical-gratings (made by Horiba Jobin Yvon) then focused onto the reaction region. In detection of the positive photoions, a supersonic molecular beam (buffered with Ar gas) installed perpendicularly to the plane containing the VUV photon beam and the time-of-flight (TOF) tube was used.…”

“…The thermodynamic values in eq are required in the interpretations to the ion-pair anion efficiency spectra (IPAES) of Cl – , − because a lot of dissociation paths may be involved in such wide energy range. Moreover, some electronic and vibrational excitations may couple with the ion-pair dissociations, showing the discrete structures or peaks in the IPAES. − Therefore, the interpretations to the IPAES and the spectral assignments heavily depend on the other spectral sources such as photoabsorption, photoelectron, and photoion mass spectra. However, only photoelectron spectra (PES) of monochlorothiophenes are available; thus, the present PIE spectra of monochlorothiophenes will play an essential role in the interpretations to the IPAES.…”

“…In this work, the chlorine anion Cl – as the product in the ion-pair dissociation of monochlorothiophenes is observed in a wide photon energy range of 10.70–22.00 eV. The thermodynamic values in eq are required in the interpretations to the ion-pair anion efficiency spectra (IPAES) of Cl – , − because a lot of dissociation paths may be involved in such wide energy range. Moreover, some electronic and vibrational excitations may couple with the ion-pair dissociations, showing the discrete structures or peaks in the IPAES. − Therefore, the interpretations to the IPAES and the spectral assignments heavily depend on the other spectral sources such as photoabsorption, photoelectron, and photoion mass spectra.…”