C O M M U N I C A T I O N S
Figure 1. Infrared spectra in the 2700-1260 cm-1 region for laser-ablated boron and 4% H2 reaction products in excess neon at 3.5 K recorded after
n
deposition, 8 K annealing, and 240-700 nm photolysis. (a) 11B, (b) B, and (c) 10B.
Table 1. Infrared Absorptions (cm-1) in Solid Neon and
orbitals. However, this H- -H bond is broken when BH2 reacts with
BH4 to form B2H6, and instead two bridged H-B-H bonds result.
Vibrational Frequencies and Infrared Intensities Calculateda for the
BH4 Radical
10B+D 11B+D 10B+H
11B+H
2
B3PW91
B3LYP
MP2
Acknowledgment. We gratefully acknowledge support from
2
2
2
2041.1 2019.6 2680.0 2666.0b 2752.7 (b2, 83)c,d 2750.3 (89) 2810.3 (83)
1890.9 1886.9 2543.3 2540.6b 2632.2 (a1, 36)c,d 2633.9 (37) 2687.0 (35)
1527.9 1518.0 2030.3 2021.4b 2149.5 (a1, 87)c,e 2112.1 (91) 2214.8 (103)
N.S.F. Grant CHE 00-78836.
References
2026.6 (b1, 0)c,e
940.2 1298.4 1298.4b 1383.5 (a1, 41)c
1040.8 (b2, 0)
1961.1 (0)
2091.3 (0.1)
940.2
1339.5 (43) 1429.2 (58)
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1051.0 (1)
969.9 (1)
743.5 (0)
694.2 (0)
1075.8 (1)
1027.5 (0)
869.8 (0)
738.4 (0)
1004.1 (a1, 0)
715.4 (b1, 0)
689.6 (a2, 0)
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a
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,
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+
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The neon matrix infrared spectrum shows that BH4 contains short
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by ESR and calculated by theory.3-9 Even though the frequencies
of this electron-deficient radical are predicted reasonably accurately,
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it is in fact of comparable intensity. The latter mode is apparently
the most difficult to model.
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electron-pair and electron-deficient B-H bonds. The two long B-H
bonds in BH4 and the included weak H- -H bond are of appropriate
length to be considered as one-electron bonds, which is substantiated
by a natural bond orbital analysis of the MP2 computed molecular
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