Fluorescence from photoexcitation of BCl3 at 45–106 nm

Abstract

The photoabsorption, fluorescence cross sections, and the fluorescence yield of BC1 3 are measured in the 45-106 nm region. Fluorescence spectra are dispersed to identify the emitting species. The emission observed at excitation wavelengths longer than 96 nm is attributed to the excited BC1!. The BCl (A-X) emission appears at excitation wavelengths shorter than 97.5 nm. Emissions observed at the thresholds of 88 and 81 nm are attributed to the excited BCI 3 + • (C 2 A ~ and D 2E') states, respectively. Emissions from excited B* atoms appear in the 48-64 nm region. In the 88-96 nm region the maxima and minima ofthe fluorescence cross section are complimentary with those of the BCI 3 + ionization yield, indicating where superexcited state(s) exist that decay through competitive channels of fluorescence and autoionization.

Vacuum UV fluorescence excitation spectroscopy of BCl3in the range 35–140 nm

“…The steep thresholds at 15.36 and 17"68 eV are in excellent agreement with the adiabatic IPs of these states (15.32 and 17.74eV respectively [4]), and the continuous nature of the fluorescence above the thresholds is characteristic of a nonresonant photoionization process because the electron can carry away the excess energy. We see no evidence for emission from the (~ 2A~ state of BCI~-(adiabatic IP = 14.22 eV) as observed by Lee et al [7], but conversely they do not see the E state emission that we observe. Fluorescence from both I3 and 1~ states occurs over a wide range of the UV and visible (Section 4.2.…”

“…The I) state emission was observed by Lee et al at inferior resolution [7] but that from the 1~ state has not been observed before. We see no evidence for the weak state emission that they report.…”

“…We have not been able to determine the range of fluorescence from the very weak peak at 13.6 eV. This peak is observed much more strongly by Lee et al [7], and they show that fluorescence at this energy is localized around 270 nm. The peak with a threshold at 15.36 eV is observed more clearly with the high-energy grating (figure 2) but we note that the fluorescence signal on the strongest low-energy peak (at 10.76eV) is about 35 times stronger than the signal on this peak.…”

“…There are limited data on the decay properties of the lowest states of BCI~-, but appearance energies for BCI~-, BCI~-and BC1 + have been measured by photoionization mass spectroscopy [5]; the value for BCI~-confirms the PES value for the adiabatic ionization potential (IP) of the X 2A~ state of the ion, and the values for BC1 f and BC1 + have been used to obtain heats of formation for these ions. The absorption and fluorescence excitation spectrum of BC13 above and below the lithium fluoride cut-off have been reported by Lee et al [6,7], and emissions assigned to both BC12 and BCI~-. In the case of BC12 no details were given of the spectroscopic properties of the electronic states which are believed to be involved.…”

“…The previous studies of fluorescence following photon or electron excitation of BC13 [6][7][8] or chemiluminescence from H + BC13 [9] have assigned the broad-band emissions to BC12. Our work supports this assignment, but suggests that the spectrum is a combination of two overlapping emissions possibly originating from the first two excited states of BC12, a similar situation to BF2 [1].…”