Vacuum ultraviolet laser pulsed field ionization photoelectron study of trans-2-butene

Abstract

The single-photon pulsed field ionization photoelectron (PFI-PE) spectrum of trans-2-butene (trans-CH3CH=CHCH3) in the energy range of 73 500–75 850 cm−1 has been measured using vacuum ultraviolet laser sources. The semi-empirical simulation of fine structures resolved in the original PFI-PE band yields a value of 73 624.7±2.0 cm−1 for the ionization energy (IE) of trans-2-butene. The vibrational bands for trans-CH3CH=CHCH3+ resolved in the PFI-PE spectrum are assigned based on ab initio calculations of the vibrational frequencies and Franck-Condon factors (FCFs) for ionization transitions. This assignment has provided reliable vibrational frequencies (ν1+=104 cm−1, ν2+=127 cm−1, ν3+=131 cm−1, ν5+=484 cm−1, ν8+=798 cm−1, ν13+=1164 cm−1, ν14+=1264 cm−1, ν16+=1307 cm−1, ν20+=1407 cm−1, and ν22+=1567 cm−1) for trans-CH3CH=CHCH3+. The PFI-PE spectrum is compared to the recently reported PFI-photoion (PFI-PI) spectrum for trans-2-butene. The major difference observed between the PFI-PE and PFI-PI spectra is that the intensities for excited vibrational bands were significantly suppressed or indiscernible in the PFI-PI spectrum, suggesting that the lifetimes for high-n Rydberg states associated with these excited vibrational bands were greatly reduced under the conditions used in the PFI-PI study. The experimental conditions used in the PFI-PI study also led to an IE value of about 20 cm−1 lower than that obtained in the PFI-PE measurement. We have also reassigned the vibrational bands resolved in the PFI-PE spectrum for cis-2-butene based on the FCF calculation and a more reliable set of theoretical vibrational frequencies.

The C3H7+ Appearance Energy from 2-Iodopropane and 2-Chloropropane Studied by Threshold Photoelectron Photoion Coincidence

“…The calculated values for the 0 K E 0 (2-C 3 H 7 + ) from 2-C 3 H 7 Cl are 11.061 and 11.048 eV obtained with ZPVE corrections at the MP2 and B3LYP levels, respectively. Considering the previous comparisons of similar calculations with highly precise PFI measurements, [18][19][20][21][22][23] we may conclude that this calculation predicts a value of 11.054 ± 0.020 eV for the 0 K AE(2-C 3 H 7 + ) from 2-C 3 H 7 Cl.…”

“…With the advance in computer capacity, it is now possible to perform high-level ab initio quantum chemical calculations for mid-size molecules such as 2-C 3 H 7 Cl. In recent studies, [18][19][20][21][22][23] we find that the complete basis set (CBS) extrapolation method at the couple cluster with single and double excitations, plus a quasi-perturbative triple excitations [CCSD(T, Full)/CBS] level of theory, 24 together with high-level corrections, generally yields reliable theoretical IE and AE predictions to within ± 20 meV compared with experimental results obtained in highly precise PFI studies. To provide insight into the reliability of the experimental AE measurements, we have also calculated the 0 K AE(2-C 3 H 7 + ) from 2-C 3 H 7 Cl at the CCSD(T, full/CBS) level with high-level corrections.…”

A Combined VUV Synchrotron Pulsed Field Ionization-Photoelectron and IR−VUV Laser Photoion Depletion Study of Ammonia

“…B. Laser Based VUV − PFI − PE Measurements. The experimental procedures for VUV−PFI−PE measurements using the VUV laser photoion-photoelectron apparatus have been described in detail previously. , In brief, the apparatus consists of a pulsed (30 Hz) tunable VUV laser system, a pulsed molecular beam source, a time-of-flight (TOF) electron spectrometer for PFI−PE detection, and a TOF mass spectrometer for ion detection. The electron spectrometer and ion mass spectrometer are each equipped with a set of microchannel plates (MCPs).…”

Vacuum Ultraviolet (VUV) Pulsed Field Ionization−Photoelectron and VUV−IR Photoinduced Rydberg Ionization Study of trans-Dichloroethene

“…Currently, the PFI−PE method represents a state-of-the-art method for vibrational spectroscopy measurements of polyatomic ions . For single-photon VUV photoionization studies, the Franck−Condon factors (FCFs) involved can be calculated by ab initio quantum chemical procedures. , Together with ab initio vibrational frequencies, the theoretical FCF spectrum has allowed the reliable assignments of most vibrational bands resolved in the VUV−PFI−PE spectra of many polyatomic molecules. ,, However, for two-photon UV PFI−PE studies, the nature of the intermediate vibronic state involved is often not known, making it difficult to perform a reliable FCF simulation. Consequently, the vibrational assignments of two-photon UV PF−PE spectra can be more complicated.…”