Dirubidium

Source: Wikipedia, the free encyclopedia.
Dirubidium
ball model of dirubidium
Identifiers
3D model (
JSmol
)
ChemSpider
  • InChI=1S/2Rb checkY
    Key: MQZGYYYBCTXEME-UHFFFAOYSA-N checkY
  • [Rb][Rb]
Properties
Rb2
Molar mass 170.9356 g·mol−1
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
 Flammable
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Dirubidium is a molecular substance containing

two atoms of rubidium found in rubidium vapour. Dirubidium has two active valence electrons. It is studied both in theory and with experiment.[1]
The rubidium trimer has also been observed.

Synthesis and properties

Dirubidium is produced when rubidium vapour is chilled. The enthalpy of formation (ΔfH°) in the gas phase is 113.29 kJ/mol.[2] In practice, an oven heated to 600 to 800K with a nozzle can squirt out vapour that condenses into dimers.[3] The proportion of Rb2 in rubidium vapour varies with its density, which depends on the temperature. At 200° the partial pressure of Rb2 is only 0.4%, at 400 °C it constitutes 1.6% of the pressure, and at 677 °C the dimer has 7.4% of the vapour pressure (13.8% by mass).[4]

The rubidium dimer has been formed on the surface of helium nanodroplets when two rubidium atoms combine to yield the dimer:

Rb + Rb → Rb2

Rb2 has also been produced in solid helium matrix under pressure.[5]

Ultracold rubidium atoms can be stored in a

exciplexes, for example Rb2(3Πu)He2 in a solid helium matrix.[7]

Ultracold rubidium dimers are being produced in order to observe quantum effects on well-defined molecules. It is possible to produce a set of molecules all rotating on the same axis with the lowest vibrational level.[8]

Spectrum

Dirubidium has several excited states, and spectral bands occur for transitions between these levels, combined with vibration. It can be studied by its absorption lines, or by laser induced-fluorescence. Laser induced-fluorescence can reveal the life-times of excited states.[1]

In the absorption spectrum of rubidium vapour, Rb2 has a major effect. Single atoms of rubidium in the vapour cause lines in the spectrum, but the dimer causes wider bands to appear. The most severe absorption between 640 and 730 nm makes the vapour almost opaque from 670 to 700 nm, wiping out the far red end of the spectrum. This is the band due to X→B transition. From 430 to 460 nm there is a shark-fin shaped absorption feature due to X→E transitions. Another shark fin like effect around 475 nm s due to X→D transitions. There is also a small hump with peaks at 601, 603 and 605.5 nm 1→3 triplet transitions and connected to the diffuse series. There are a few more small absorption features in the near infrared.[9]

There is also a dirubidium cation, Rb2+ with different spectroscopic properties.[1]

Bands

Transition Colour Known vibrational bands Bandheads
A-X infrared
B-X red 4-0 5-0 6-0 7-0 8-0 9-0 10-0 11-0 6-1 7-1 8-1 9-2 14847.080 to 15162.002
C-X blue
D-X blue-violet
1-C infrared
C→2 6800–8000 cm−1
11Δg-X 540 nm quadrupole

Molecular constants for excited states

The following table has parameters for 85Rb85Rb the most common for the natural element.

Parameter Te ωe ωexe ωeye Be αe γe De βe re ν00 Re Å ref
31Σg+ 5.4 Å [10]
43+
u 5s+6s
33Δu 5s+4d
33Πu 5s + 6p 22 610.27 41.4 [11]
23Πu 19805.2 42.0 0.01841 4.6 [11]
13Σg 5p+5s
13Σu 5p+5s weak [5]
13Πu 5p+5s
2g 13029.29 0.01568 5.0 [12]
1g 13008.610 0.0158 5.05 [12]
0−
g		 12980.840 0.0151 5.05 [6][12]
0+
g inner		 12979.282 0.015489 5.1 [12]
0+
g outer		 13005.612 0.00478 9.2 [12]
0+
u		 [6][12]
c3Σu+ (unbound) 5p2P3/2 [13]
b3Πu
b3Π0u+ 9600.83 60.10 4.13157 Å [14]
a3Σu+ metastable triplet [6]
a3Πu triplet ground state [6]
141Σg+ 30121.0 44.9 0.01166 pred[11]
131Σg+ 28 863.0 46.1 0.01673 pred[11]
121Σg+ 28 533.9 38.4 0.01656 pred[11]
111Σg+ 28 349.9 42.0 0.01721 pred[11]
101Σg+ 27 433.1 45.3 0.01491 pred[11]
91Σg+ 26 967.1 45.1 0.01768 pred[11]
81Σg+ 26 852.9 44.6 0.01724 pred[11]
71Σg+ 25 773.9 76.7 0.01158 pred[11]
61Σg+ 24 610.8 46.3 0.01800 pred[11]
111Σu+ 29 709.4 41.7 0.01623 pred[11]
101Σu+ 29 339.2 35.0 0.016 85 pred[11]
91Σu+ 28 689.9 43.6 0.01661 pred[11]
81Σu+ 28 147.3 51.5 0.01588 pred[11]
71Σu+ 27 716.8 44.5 0.01636 pred[11]
61Σu+ 26 935.8 49.6 0.01341 pred[11]
51Σu+ 26108.8 39 0.016 47 4.9 [11][15]
51Πu 26131 4.95 [15]
41Σu+ 24 800.8 10.7 0.00298 pred[11]
41Σg+ 20004.13 61.296 0.01643 [11]
31Σu+ 5s+6s 22 405.2 40.2 0.015 536 [11]
31Πu = D1Πu 5s + 6p 22777.53 36.255 0.01837 5008.59 4.9 Å [16]
21Σg+ 13601.58 31.4884 -0.01062 0.013430 -0.0000018924 2963 5.4379 [17]
21Σu+ 6s+4d 5.5 (vibration causes a large stretching) [6]
21Πu = C1Πu 20 913.18 36.255 0.01837 [11]
21Πg 22 084.9 30.6 0.01441 [11]
11Δg
11Πu
11Πg 15510.28 22.202 -0.1525 0.013525 -0.0001209 1290 cm−1 5.418 [13]
B1Πu 5s+5p 14665.44 47.4316 0.1533 0.0060 0.01999 0.000070 1.4 [3]
A1Σu+ 5s+5p 10749.742 44.58 4.87368 Å [14]
X1Σg+ 5s+5s 12816 57.7467 0.1582 0.0015 0.02278 0.000047 1.5/3986 cm−1 4.17 [3][17]

Related species

The other alkali metals also form dimers: dilithium Li2, Na2, K2, and Cs2. The rubidium trimer has also been observed on the surface of helium nanodroplets. The trimer, Rb3 has the shape of an equilateral triangle, bond length of 5.52 A˚ and a binding energy of 929 cm−1.[18]

References

  1. ^
    S2CID 250784871
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  2. ^ Chase, M. W. (1998). "Dirubidium". webbook.nist.gov: 1–1951.
  3. ^
    doi:10.1016/0301-0104(80)80031-0
    .
  4. doi:10.1016/j.jqsrt.2018.01.003
    .
  5. ^
    S2CID 53701950
    .
  6. ^
    S2CID 52970920
    .
  7. S2CID 53701950
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  8. hdl:1969.1/180938
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  9. doi:10.1016/j.optcom.2006.06.070
    .
  10. PMID 26772572
    .
  11. ^
    PMID 26233130
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  12. ^
    PMID 21909578
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  13. ^
    doi:10.1080/00268978600101491
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  14. ^
    doi:10.1103/PhysRevA.80.022515
    .
  15. ^
    doi:10.1016/j.jqsrt.2017.08.011
    .
  16. doi:10.1016/j.jms.2016.06.010
    .
  17. ^
    doi:10.1080/00268978700100981
    .
  18. PMID 18352466
    .
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