Dirubidium

Last updated
Dirubidium
Dirubidium-2D-dimensions.png
Dirubidium-3D-vdW.png
Identifiers
3D model (JSmol)
ChemSpider
PubChem CID
  • InChI=1S/2Rb Yes check.svgY
    Key: MQZGYYYBCTXEME-UHFFFAOYSA-N Yes check.svgY
  • [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.

Contents

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 magneto-optic trap and then photoassociated to form molecules in an excited state, vibrating at a rate so high they barely hang together. [6] In solid matrix traps, Rb2 can combine with the host atoms when excited to form 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

TransitionColourKnown vibrational bandsBandheads
A-Xinfrared
B-Xred4-0 5-0 6-0 7-0 8-0 9-0 10-0 11-0 6-1 7-1 8-1 9-214847.080 to 15162.002
C-Xblue
D-Xblue-violet
1-Cinfrared
C→26800–8000 cm−1
11Δg-X540 nm quadrupole

Molecular constants for excited states

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

ParameterTeωeωexeωeyeBeαeγeDeβereν00Re Åref
31Σg+5.4 Å [10]
43+
u 5s+6s
33Δu 5s+4d
33Πu 5s + 6p22 610.2741.4 [11]
23Πu19805.242.00.018414.6 [11]
13Σg 5p+5s
13Σu 5p+5sweak [5]
13Πu 5p+5s
2g13029.290.015685.0 [12]
1g13008.6100.01585.05 [12]
0−
g		12980.8400.01515.05 [6] [12]
0+
g inner		12979.2820.0154895.1 [12]
0+
g outer		13005.6120.004789.2 [12]
0+
u		 [6] [12]
c3Σu+ (unbound) 5p2P3/2 [13]
b3Πu
b3Π0u+9600.8360.104.13157 Å [14]
a3Σu+ metastable triplet [6]
a3Πu triplet ground state [6]
141Σg+30121.044.90.01166pred [11]
131Σg+28 863.046.10.01673pred [11]
121Σg+28 533.938.40.01656pred [11]
111Σg+28 349.942.00.01721pred [11]
101Σg+27 433.145.30.01491pred [11]
91Σg+26 967.145.10.01768pred [11]
81Σg+26 852.944.60.01724pred [11]
71Σg+25 773.976.70.01158pred [11]
61Σg+24 610.846.30.01800pred [11]
111Σu+29 709.441.70.01623pred [11]
101Σu+29 339.235.00.016 85pred [11]
91Σu+28 689.943.60.01661pred [11]
81Σu+28 147.351.50.01588pred [11]
71Σu+27 716.844.50.01636pred [11]
61Σu+26 935.849.60.01341pred [11]
51Σu+26108.8390.016 474.9 [11] [15]
51Πu261314.95 [15]
41Σu+24 800.810.70.00298pred [11]
41Σg+20004.1361.2960.01643 [11]
31Σu+ 5s+6s22 405.240.20.015 536 [11]
31Πu = D1Πu 5s + 6p22777.5336.2550.018375008.594.9 Å [16]
21Σg+13601.5831.4884-0.010620.013430-0.000001892429635.4379 [17]
21Σu+ 6s+4d5.5 (vibration causes a large stretching) [6]
21Πu = C1Πu20 913.1836.2550.01837 [11]
21Πg22 084.930.60.01441 [11]
11Δg
11Πu
11Πg15510.2822.202-0.15250.013525-0.00012091290 cm−15.418 [13]
B1Πu 5s+5p14665.4447.43160.15330.00600.019990.0000701.4 [3]
A1Σu+ 5s+5p10749.74244.584.87368 Å [14]
X1Σg+ 5s+5s1281657.74670.15820.00150.022780.0000471.5/3986 cm−14.17 [3] [17]

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]

Related Research Articles

<span class="mw-page-title-main">Spectroscopy</span> Study involving matter and electromagnetic radiation

Spectroscopy is the field of study that measures and interprets the electromagnetic spectra that result from the interaction between electromagnetic radiation and matter as a function of the wavelength or frequency of the radiation. Matter waves and acoustic waves can also be considered forms of radiative energy, and recently gravitational waves have been associated with a spectral signature in the context of the Laser Interferometer Gravitational-Wave Observatory (LIGO).

<span class="mw-page-title-main">Spectral line</span> A distinctive narrow spectral feature of chemical species

A spectral line is a weaker or stronger region in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used to identify atoms and molecules. These "fingerprints" can be compared to the previously collected ones of atoms and molecules, and are thus used to identify the atomic and molecular components of stars and planets, which would otherwise be impossible.

Dilithium, Li2, is a strongly electrophilic, diatomic molecule comprising two lithium atoms covalently bonded together. Li2 is known in the gas phase. It has a bond order of 1, an internuclear separation of 267.3 pm and a bond energy of 102 kJ/mol or 1.06 eV in each bond. The electron configuration of Li2 may be written as σ2.

<span class="mw-page-title-main">Fluorophore</span> Agents that emit light after excitation by light

A fluorophore is a fluorescent chemical compound that can re-emit light upon light excitation. Fluorophores typically contain several combined aromatic groups, or planar or cyclic molecules with several π bonds.

<span class="mw-page-title-main">Morse potential</span> Model for the potential energy of a diatomic molecule

The Morse potential, named after physicist Philip M. Morse, is a convenient interatomic interaction model for the potential energy of a diatomic molecule. It is a better approximation for the vibrational structure of the molecule than the quantum harmonic oscillator because it explicitly includes the effects of bond breaking, such as the existence of unbound states. It also accounts for the anharmonicity of real bonds and the non-zero transition probability for overtone and combination bands. The Morse potential can also be used to model other interactions such as the interaction between an atom and a surface. Due to its simplicity, it is not used in modern spectroscopy. However, its mathematical form inspired the MLR (Morse/Long-range) potential, which is the most popular potential energy function used for fitting spectroscopic data.

<span class="mw-page-title-main">Doppler cooling</span> Laser cooling technique

Doppler cooling is a mechanism that can be used to trap and slow the motion of atoms to cool a substance. The term is sometimes used synonymously with laser cooling, though laser cooling includes other techniques.

<span class="mw-page-title-main">Two-photon absorption</span> Simultaneous absorption of two photons by a molecule

In atomic physics, two-photon absorption, also called two-photon excitation or non-linear absorption, is the simultaneous absorption of two photons of identical or different frequencies in order to excite a molecule from one state to a higher energy, most commonly an excited electronic state. Absorption of two photons with different frequencies is called non-degenerate two-photon absorption. Since TPA depends on the simultaneous absorption of two photons, the probability of TPA is proportional to the square of the light intensity; thus it is a nonlinear optical process. The energy difference between the involved lower and upper states of the molecule is equal or smaller than the sum of the photon energies of the two photons absorbed. Two-photon absorption is a third-order process, with absorption cross section typically several orders of magnitude smaller than one-photon absorption cross section.

Photoelectrochemical processes are processes in photoelectrochemistry; they usually involve transforming light into other forms of energy. These processes apply to photochemistry, optically pumped lasers, sensitized solar cells, luminescence, and photochromism.

The technique of vibrational analysis with scanning probe microscopy allows probing vibrational properties of materials at the submicrometer scale, and even of individual molecules. This is accomplished by integrating scanning probe microscopy (SPM) and vibrational spectroscopy. This combination allows for much higher spatial resolution than can be achieved with conventional Raman/FTIR instrumentation. The technique is also nondestructive, requires non-extensive sample preparation, and provides more contrast such as intensity contrast, polarization contrast and wavelength contrast, as well as providing specific chemical information and topography images simultaneously.

The Hanle effect, also known as zero-field level crossing, is a reduction in the polarization of light when the atoms emitting the light are subject to a magnetic field in a particular direction, and when they have themselves been excited by polarized light.

<span class="mw-page-title-main">Chromium(I) hydride</span> Chemical compound

Chromium(I) hydride, systematically named chromium hydride, is an inorganic compound with the chemical formula (CrH)
n. It occurs naturally in some kinds of stars where it has been detected by its spectrum. However, molecular chromium(I) hydride with the formula CrH has been isolated in solid gas matrices. The molecular hydride is very reactive. As such the compound is not well characterised, although many of its properties have been calculated via computational chemistry.

In spectroscopy, collision-induced absorption and emission refers to spectral features generated by inelastic collisions of molecules in a gas. Such inelastic collisions may induce quantum transitions in the molecules, or the molecules may form transient supramolecular complexes with spectral features different from the underlying molecules. Collision-induced absorption and emission is particularly important in dense gases, such as hydrogen and helium clouds found in astronomical systems.

<span class="mw-page-title-main">Calcium monohydride</span> Chemical compound

Calcium monohydride is a molecule composed of calcium and hydrogen with formula CaH. It can be found in stars as a gas formed when calcium atoms are present with hydrogen atoms.

LiHe is a compound of helium and lithium. The substance is a cold low-density gas made of Van der Waals molecules, each composed of a helium atom and lithium atom bound by van der Waals force. The preparation of LiHe opens up the possibility to prepare other helium dimers, and beyond that multi-atom clusters that could be used to investigate Efimov states and Casimir retardation effects.

<span class="mw-page-title-main">Helium dimer</span> Chemical compound

The helium dimer is a van der Waals molecule with formula He2 consisting of two helium atoms. This chemical is the largest diatomic molecule—a molecule consisting of two atoms bonded together. The bond that holds this dimer together is so weak that it will break if the molecule rotates, or vibrates too much. It can only exist at very low cryogenic temperatures.

Helium is the smallest and the lightest noble gas and one of the most unreactive elements, so it was commonly considered that helium compounds cannot exist at all, or at least under normal conditions. Helium's first ionization energy of 24.57 eV is the highest of any element. Helium has a complete shell of electrons, and in this form the atom does not readily accept any extra electrons nor join with anything to make covalent compounds. The electron affinity is 0.080 eV, which is very close to zero. The helium atom is small with the radius of the outer electron shell at 0.29 Å. Helium is a very hard atom with a Pearson hardness of 12.3 eV. It has the lowest polarizability of any kind of atom, however, very weak van der Waals forces exist between helium and other atoms. This force may exceed repulsive forces, so at extremely low temperatures helium may form van der Waals molecules. Helium has the lowest boiling point of any known substance.

<span class="mw-page-title-main">Helium trimer</span> Chemical compound

The helium trimer is a weakly bound molecule consisting of three helium atoms. Van der Waals forces link the atoms together. The combination of three atoms is much more stable than the two-atom helium dimer. The three-atom combination of helium-4 atoms is an Efimov state. Helium-3 is predicted to form a trimer, although ground state dimers containing helium-3 are completely unstable.

Neon compounds are chemical compounds containing the element neon (Ne) with other molecules or elements from the periodic table. Compounds of the noble gas neon were believed not to exist, but there are now known to be molecular ions containing neon, as well as temporary excited neon-containing molecules called excimers. Several neutral neon molecules have also been predicted to be stable, but are yet to be discovered in nature. Neon has been shown to crystallize with other substances and form clathrates or Van der Waals solids.

Argon compounds, the chemical compounds that contain the element argon, are rarely encountered due to the inertness of the argon atom. However, compounds of argon have been detected in inert gas matrix isolation, cold gases, and plasmas, and molecular ions containing argon have been made and also detected in space. One solid interstitial compound of argon, Ar1C60 is stable at room temperature. Ar1C60 was discovered by the CSIRO.

<span class="mw-page-title-main">Diargon</span> Chemical compound

Diargon or the argon dimer is a molecule containing two argon atoms. Normally, this is only very weakly bound together by van der Waals forces. However, in an excited state, or ionised state, the two atoms can be more tightly bound together, with significant spectral features. At cryogenic temperatures, argon gas can have a few percent of diargon molecules.

References

  1. 1 2 3 Spiegelmann, F; Pavolini, D; Daudey, J -P (28 August 1989). "Theoretical study of the excited states of the heavier alkali dimers. II. The Rb molecule". Journal of Physics B: Atomic, Molecular and Optical Physics. 22 (16): 2465–2483. Bibcode:1989JPhB...22.2465S. doi:10.1088/0953-4075/22/16/005. S2CID   250784871.
  2. ↑ Chase, M. W. (1998). "Dirubidium". webbook.nist.gov: 1–1951.
  3. 1 2 3 Caldwell, C.D.; Engelke, F.; Hage, H. (December 1980). "High resolution spectroscopy in supersonic nozzle beams: The Rb2 B 1Πu-X 1Σ+g band system". Chemical Physics. 54 (1): 21–31. Bibcode:1980CP.....54...21C. doi:10.1016/0301-0104(80)80031-0.
  4. ↑ Rakića, M.; Pichler, G. (March 2008). "Photoionization bands of rubidium molecule". Journal of Quantitative Spectroscopy and Radiative Transfer. 208: 39–44. Bibcode:2018JQSRT.208...39R. doi:10.1016/j.jqsrt.2018.01.003.
  5. 1 2 Moroshkin, P.; Hofer, A.; Ulzega, S.; Weis, A. (7 September 2006). "Spectroscopy of Rb2 dimers in solid". Physical Review A. 74 (3): 032504. arXiv: physics/0606100 . Bibcode:2006PhRvA..74c2504M. doi:10.1103/PhysRevA.74.032504. S2CID   53701950.
  6. 1 2 3 4 5 6 Huang, Y; Qi, J; Pechkis, H K; Wang, D; Eyler, E E; Gould, P L; Stwalley, W C (14 October 2006). "Formation, detection and spectroscopy of ultracold Rb2 in the ground X 1Σg state". Journal of Physics B: Atomic, Molecular and Optical Physics. 39 (19): S857–S869. Bibcode:2006JPhB...39S.857H. doi:10.1088/0953-4075/39/19/S04. S2CID   52970920.
  7. ↑ Moroshkin, P.; Hofer, A.; Ulzega, S.; Weis, A. (7 September 2006). "Spectroscopy of Rb2 dimers in solid 4He". Physical Review A. 74 (3). arXiv: physics/0606100 . Bibcode:2006PhRvA..74c2504M. doi:10.1103/PhysRevA.74.032504. S2CID   53701950.
  8. ↑ Shore, Bruce W; Dömötör, Piroska; Sadurní, Emerson; Süssmann, Georg; Schleich, Wolfgang P (27 January 2015). "Scattering of a particle with internal structure from a single slit". New Journal of Physics. 17 (1): 013046. Bibcode:2015NJPh...17a3046S. doi: 10.1088/1367-2630/17/1/013046 . hdl: 1969.1/180938 .
  9. ↑ Vdović, S.; Sarkisyan, D.; Pichler, G. (December 2006). "Absorption spectrum of rubidium and cesium dimers by compact computer operated spectrometer". Optics Communications. 268 (1): 58–63. Bibcode:2006OptCo.268...58V. doi:10.1016/j.optcom.2006.06.070.
  10. ↑ Yang, Jinxin; Guan, Yafei; Zhao, Wei; Zhou, Zhaoyu; Han, Xiaomin; Ma, Jie; Sovkov, Vladimir B.; Ivanov, Valery S.; Ahmed, Ergin H.; Lyyra, A. Marjatta; Dai, Xingcan (14 January 2016). "Observations and analysis with the spline-based Rydberg–Klein–Rees approach for the 31Σg+ state of Rb2". The Journal of Chemical Physics. 144 (2): 024308. Bibcode:2016JChPh.144b4308Y. doi:10.1063/1.4939524. PMID   26772572.
  11. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 Jastrzebski, Wlodzimierz; Kowalczyk, Pawel; Szczepkowski, Jacek; Allouche, Abdul-Rahman; Crozet, Patrick; Ross, Amanda J. (28 July 2015). "High-lying electronic states of the rubidium dimer – predictions and experimental observation of the 51Σu+ and 5 Π states of Rb by polarization labelling spectroscopy". The Journal of Chemical Physics. 143 (4): 044308. Bibcode:2015JChPh.143d4308J. doi:10.1063/1.4927225. PMID   26233130.
  12. 1 2 3 4 5 6 Bellos, M. A.; Rahmlow, D.; Carollo, R.; Banerjee, J.; Dulieu, O.; Gerdes, A.; Eyler, E. E.; Gould, P. L.; Stwalley, W. C. (2011). "Formation of ultracold Rb2 molecules in the v′′ = 0 level of the a3Σ+u state via blue-detuned photoassociation to the 13Πg state". Physical Chemistry Chemical Physics. 13 (42): 18880–18886. Bibcode:2011PCCP...1318880B. doi:10.1039/C1CP21383K. PMID   21909578.
  13. 1 2 Amiot, C. (July 1986). "The Rb2 1 1Πg electronic state by laser-induced fluorescence infrared Fourier transform spectroscopy". Molecular Physics. 58 (4): 667–678. Bibcode:1986MolPh..58..667A. doi:10.1080/00268978600101491.
  14. 1 2 Salami, H.; Bergeman, T.; Beser, B.; Bai, J.; Ahmed, E. H.; Kotochigova, S.; Lyyra, A. M.; Huennekens, J.; Lisdat, C.; Stolyarov, A. V.; Dulieu, O.; Crozet, P.; Ross, A. J. (27 August 2009). "Spectroscopic observations, spin-orbit functions, and coupled-channel deperturbation analysis of data on the A1sigma+u and b3piu states of Rb2". Physical Review A. 80 (2): 022515. Bibcode:2009PhRvA..80b2515S. doi:10.1103/PhysRevA.80.022515.
  15. 1 2 Havalyova, I.; Pashov, A.; Kowalczyk, P.; Szczepkowski, J.; Jastrzebski, W. (November 2017). "The coupled system of (5)1sigmau+ and (5) 1 Π u electronic states in Rb 2". Journal of Quantitative Spectroscopy and Radiative Transfer. 202: 328–334. Bibcode:2017JQSRT.202..328H. doi:10.1016/j.jqsrt.2017.08.011.
  16. ↑ Jastrzebski, W.; Kowalczyk, P. (December 2016). "Potential energy curve of the D(3) 1Πu state in rubidium dimer from spectroscopic measurements". Journal of Molecular Spectroscopy. 330: 96–100. Bibcode:2016JMoSp.330...96J. doi:10.1016/j.jms.2016.06.010.
  17. 1 2 Amiot, C.; Verges, J. (May 1987). "The Rb2 21Σ+g electronic state by laser induced fluorescence infrared Fourier transform spectroscopy". Molecular Physics. 61 (1): 51–63. Bibcode:1987MolPh..61...51A. doi:10.1080/00268978700100981.
  18. ↑ Nagl, Johann; Auböck, Gerald; Hauser, Andreas W.; Allard, Olivier; Callegari, Carlo; Ernst, Wolfgang E. (13 February 2008). "Heteronuclear and Homonuclear High-Spin Alkali Trimers on Helium Nanodroplets". Physical Review Letters. 100 (6): 063001. Bibcode:2008PhRvL.100f3001N. doi:10.1103/PhysRevLett.100.063001. PMID   18352466.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.