The electronic spectrum of Si₃ I: Triplet D_3h system

M. C.

 

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C. A.

 

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, and

P.

 

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M.

 

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J.

 

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J.

 

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P. W.

 

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J. P.

 

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,

N. M.

 

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, and

D. A.

 

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I.

 

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S.

 

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, and

J. R.

 

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B. K.

 

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, and

S. N.

 

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S.

 

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R. J. V.

 

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J. W.

 

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, and

K.

 

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,  , ().

C. S.

 

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,

T. R.

 

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G. R.

 

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, and

D. M.

 

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,  , ().

E. B.

 

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and

J. P.

 

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K.

 

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and

V.

 

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K.

 

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R. S.

 

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and

H. F.

 

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 III,  , ().

C. M.

 

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and

K.

 

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J.

 

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M. C.

 

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and

P.

 

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,  , ().

F. J.

 

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T. N.

 

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C. C.

 

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J. L.

 

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M. C.

 

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A. C.

 

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K. A.

 

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and

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P. O.

 

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P. A.

 

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, and

B. O.

 

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CFOUR, a quantum chemical program package written by

J. F.

 

Stanton

,

J.

 

Gauss

,

M. E.

 

Harding

,

P. G.

 

Szalay

with contributions from

A. A.

 

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,

R. J.

 

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U.

 

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,

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L. A.

 

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and the integral packages MOLECULE (

J.

 

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and

P. R.

 

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), PROPS (

P. R.

 

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), ABACUS (

T.

 

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,

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, and

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), and ECP routines by

A. V.

 

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and

C.

 

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. For the current version, see http://www.cfour.de.

D. H.

 

Shi

,

J. F.

 

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,

Z. L.

 

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, and

Y. F.

 

Liu

,  , ().

M.

 

Fukushima

,

S.

 

Mayama

, and

K.

 

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,  , ().

The strongest feature in Fig. 4 is the

$1_0^1$

$101$

$2_0^2$

$202$ band of the

$\tilde{A}$

$Ã$ ¹B₁ – 

$\tilde{X}$

$X̃$ ¹A₁ transition of SiH₂, as reported by Ishikawa and Kajimoto.³⁹ SiH₂ has harmonic bending frequencies in its

$\tilde{X}$

$X̃$ ¹A₁and

$\tilde{A}$

$Ã$ ¹B₁ states of 1000 cm⁻¹and 854 cm⁻¹, respectively.³⁷ Its

$1_0^1$

$101$

$2_1^3$

$213$ hot band thus occurs near 19040 cm⁻¹, coincident with the Si₃

$1_0^1$

$101$ band, and can emit to the blue of the laser in the DF spectrum. (Levels involving the bending mode of SiH₂ also coincide with the Si₃1₂ level in this DF spectrum, so a Franck-Condon simulation of the Si₃ DF intensities has little value.) Under slightly different expansion conditions, this hot band was extremely strong in survey LIF spectra. The observed Si₃ fluorescence decay profile is characterized by a single exponential with a lifetime - about 1 μs - similar to that of SiH₂, so fluorescence from the latter cannot be temporally gated out. While a definitive assignment of the particular lower state involved in the blue-shifted transition is not obvious, there are several transitions of SiH₂ near 19 750 cm⁻¹that could produce the appropriate blue-shift, within the monochromator resolution.³⁹ Moreover, no transitions of Si₃ were observed when the laser was scanned with the monochromator fixed over the blue-shifted feature, and no such feature appears at the same blue-shift in DF spectra from the Si₃ origin and sequence bands. It thus seems unlikely that this blue-shifted feature comes from Si₃; in particular, it is not associated with the triplet system studied here.

H.

 

Ishikawa

and

O.

 

Kajimoto

,  , ().

N. J.

 

Reilly

,

T. W.

 

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, and

S. H.

 

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,  , ().

N. J.

 

Reilly

,

D. L.

 

Kokkin

,

M.

 

Nakajima

,

K.

 

Nauta

,

S. H.

 

Kable

, and

T. W.

 

Schmidt

,  , ().