I think it depends on how you choose to define a “direct observation”. If you define the term too strictly, then you’d be hard pressed to find things that can be directly observed in chemistry… and thus this statement is not saying much. However, if you are using a looser definition that is more compatible with standard techniques in chemistry in which signals are correlated to structures and dynamics (NMR, TIRF, AFM, etc…), then here you may find a few examples of direct observations of molecular orbitals:
Itatani, Jiro, et al. “Tomographic imaging of molecular orbitals.” Nature 432.7019 (2004): 867.
Zhai, Chunyang, et al. “Coulomb-corrected molecular orbital tomography of nitrogen.” Scientific reports 6 (2016).
Soe, W-H., et al. “Direct observation of molecular orbitals of pentacene physisorbed on Au (111) by scanning tunneling microscope.” Physical review letters 102.17 (2009): 176102.
Observation of electron density which can be traced to (arbitrary) selection of orbitals is indeed possible, but why would the angular part of an orbital, i.e. a spherical harmonic function be observed and not a Bloch function or a Hankel spherical function?
The claim is just to sketchy for me.
Thanks for pointing these papers out. Have a nice day
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Dr. Joaquin Barroso's Blog 
Explain why orbitals can’t observed??
J. Am. Chem. Soc. 2015, 137, 14743.
I think it depends on how you choose to define a “direct observation”. If you define the term too strictly, then you’d be hard pressed to find things that can be directly observed in chemistry… and thus this statement is not saying much. However, if you are using a looser definition that is more compatible with standard techniques in chemistry in which signals are correlated to structures and dynamics (NMR, TIRF, AFM, etc…), then here you may find a few examples of direct observations of molecular orbitals:
Itatani, Jiro, et al. “Tomographic imaging of molecular orbitals.” Nature 432.7019 (2004): 867.
Zhai, Chunyang, et al. “Coulomb-corrected molecular orbital tomography of nitrogen.” Scientific reports 6 (2016).
Soe, W-H., et al. “Direct observation of molecular orbitals of pentacene physisorbed on Au (111) by scanning tunneling microscope.” Physical review letters 102.17 (2009): 176102.
Suzuki, Toshinori. “Femtosecond time-resolved photoelectron imaging.” Annu. Rev. Phys. Chem. 57 (2006): 555-592.
Observation of electron density which can be traced to (arbitrary) selection of orbitals is indeed possible, but why would the angular part of an orbital, i.e. a spherical harmonic function be observed and not a Bloch function or a Hankel spherical function?
The claim is just to sketchy for me.
Thanks for pointing these papers out. Have a nice day
I see you don’t monetize your site, don’t waste your traffic, you can earn additional bucks every month because you’ve got
hi quality content. If you want to know how to make extra money, search for: best adsense alternative
Wrastain’s tools