Penning ionization electron spectrometry of hydrogen chloride

Abstract

An electron spectrometric study has been performed on HC1 using metastable helium and neon atoms as well as neon resonance photons. High resolution electron spectra were obtained with two different beam apparatuses for a mixed He(2 ~S, 23S) beam, a pure He(23S) beam, and, for the first time, state-selected pure Ne(3s3P2) and pure Ne(3s3P0) beams, and for NeI resonance photons. For the system He(23S)+HC1 the vibrational populations P(v') of the formed HCI+(X2//i, v') and HCI+(A 2L'+, v') ions are found to differ from the Franck-Condon factors for unperturbed potentials, indicating slight bond stretching in HC1 upon He(2 3S) approach. For He(21S) + HC1 the vibrational peak shapes and vibrational populations are substantially different from the He(2aS) case, pointing to an additional, charge exchanged interaction (He ÷ +HC1-) in the entrance channel of the former system. For the first time, we have detected the electrons in both the He(21S) + HC1 and He(2 3S) + HC1 spectra associated with the major mechanism for the formation of C1 ÷ ions: energy transfer to repulsive HCI** Rydberg states, dissociating to H(1 s) and autoionizing Ct**(1D2 n/) atoms. For both Ne (3P2)+ HC1 and Ne(3Po)+HC1, the populations P(v') of both final molecular states HCI+(X, A) agree closely with the Franck-Condon factors at the average relative collision energy E~oll = 55 meV and, for HCt + (A 2S+), also at E~o n = 130 meV.

Penning ionization and photoionization electron spectrometry of hydrogen fluoride

“…For example, our results show a decrease in the normalized, relative transition probability P(v') for v ' = 1 formation from 36.0 in photoionization to 26.9 in PI, suggesting a slight bond stretching in HF in the incoming He (2 3S)/HF potential. This conclusion was similarly arrived at in our previous He'(2 3S) PI studies of HC1 [31] and HBr [32]. From a comparison of the vibrational spacings given in Table 2 observed in HF ~ (X2H~) formation, good agreement is found between our values derived from He (2 3S) PI of HF and HeI photoionization of HF and generally good agreement with similar studies (PES) and by other methods, including calculated results.…”

“…4, but a reliable analysis is hampered below 3.8 eV electron energy due to difficulties encountered in subtracting the large signals due to HF + (X2H~, v ' = 0) formation by He(2 3S) metastables in the two spectra. We conclude here, as we did previously in the analysis of the He (2 ~S) PI spectra of HC1 [31] and HBr [32], that each vibrational Penning peak is made up of a narrow, "normal" peak (like in He (2 3S) PI) and a broad peak with an extensive low-energy tail. Our fitting procedure utilized identical, simple Gaussians for the narrow components (FWHM = 125 meV, see dashed curves in Fig.…”

“…Finally, we point out that there is an absence of atomicline autoionizing structure in the low electron-energy region of the metastable spectra (top and middle traces in Fig. 1) in contrast to their prominence in the PI spectra of HC1 [31], HBr [32] and HI [33]. From an inspection of the HF + potential-energy curves given by Raftery and Richards ( Fig.…”

“…2). Based on our experience in deconvoluting vibrationalband fine-structure components in HC1 [31] and HBr [32], we have successfully deconvoluted the very broad Penning structure in Fig. 4 (left side) into the v' = 0 fine- The spectrum is obtained by subtracting the pure He(2 3S) produced spectrum from the mixed He (2 1'3S) metastable spectrum (see Fig.…”

“…The experimental apparatus and the procedure for taking electron spectra with different excitation sources has been described in detail previously [31,32], so only a brief overview will be given here. The apparatus consisted of two differentially-pumped chambers with base pressures of < 2.10 .7 Torr, each evacuated by a separate 5001 s-1 turbomolecular pump.…”