The infrared spectra of BF3+ and BF2OH+ trapped in solid neon

Abstract

Observations on a Ne:BF(3) = 400:1 mixture into which a trace of normal or isotopically enriched water had been introduced, codeposited at 4.3 K with a beam of neon atoms that had been excited in a microwave discharge, demonstrate that a pair of absorptions at 1662 cm(-1) and 1722 cm(-1) that were previously assigned to the two boron-isotopic species of BF(3)(+) should be reassigned to a BF(2) stretching fundamental of BF(2)OH(+). The OH stretching fundamental of that product was identified for the first time at 3240 cm(-1). The degenerate BF(3) stretching fundamental of (11)BF(3)(+) appears at an unusually high frequency, 1790 cm(-1), consistent with strong pseudo-Jahn-Teller interaction of that ground-state fundamental with the B̃(2)E(') electronic state, as predicted by theory. The recent availability of detailed ab initio and density functional calculations of the vibrational fundamentals of BF(2)(-) and BF(3)(-) facilitates assignment of the infrared absorptions of those two products.

Ground and excited states of BF3+. Coupled cluster and density functional studies

“…In 2S1L the short BF bond distance r 2 is 1.2441 Å, and the vibrational b 2 frequency is 1895 cm À1 (CCSD values, Tables 1 and 5). For BF 2 + trapped in solid neon, a frequency of 2026.1 cm À1 was found [8]. According to CCSD calculations, BF 2 + (linear) has a bond distance of 1.2221 Å and a highest vibrational frequency of 2092 cm À1 (r u ), close to the experimental value and to the frequency observed in BF 3 + .…”

“…Vibrational frequencies of 509.6 cm À1 (out-of-plane) and 1790.8 cm À1 (BF 3 stretch) were reported for 11 BF 3 + [8]. Calculated harmonic frequencies for 1S2L and 2S1L found by the CCSD method are shown in Table 5, and very similar LC-B97D values in Table 6.…”

“…The calculated value for the short B-F distance is $1.25 Å, for the long B-F distance $1.41 Å, and for the F(axial)-B-F angle $108°. Jacox and Thompson [8] observed for 11 BF 3 + vibrational frequencies of 509.6 cm À1 (out-ofplane) and 1790.8 cm À1 (BF 3 stretch), and noted that the unusually high frequency for the BF 3 + stretching fundamental is consistent with a strong PJT interaction of the 1 2 A 2 0 ground state with 2 E 0 excited states. An absorption at 1661.6 cm À1 , initially assigned to 11 BF 3 + [9], was later reassigned to BF 2 OH + .…”

“…The highest oscillator strengths f were found in the case of 1S2L for excitation to 1 2 A 1 , having a VEE of 2.45 eV with f = 0.073, and to 2 2 A 1 at 5.61 eV with f = 0.09; in the Table 6 LC-B97D harmonic frequencies m (cm À1 ) and IR intensities (km/mol) for 11 BF 3 + at C 2v symmetry. Experimental values [8] bold, in parentheses. There is a distinct gap in VEEs between these two groups of excited states.…”

“…Jacox and Thompson [8] assumed BF 3 + to be close to a complex of BF 2 + with F, corresponding to a lengthening of the BF axial bond, and shortening of the other two BF bonds (2S1L), in agreement with the structure proposed by Haller et al [7]. In 2S1L the short BF bond distance r 2 is 1.2441 Å, and the vibrational b 2 frequency is 1895 cm À1 (CCSD values, Tables 1 and 5).…”