Molecular matters van der Waals molecules: 1. History and some perspectives on intermolecular forces

van der waals introduced his equation of state in 1867 modifying the ideal gas equation. His equation had two constants a and b, which accounted for the fact that molecules have attractive forces and finite size. The constant a accounted for the attractive forces, the nature of which was not outlined by van der waals. This series of articles will discuss about the nature of intermolecular forces

Molecule matters van der Waals molecules: 2. Noble gas clusters are London molecules!

In Part 2 of this series, we discuss homo- and hetero-nuclear noble gas dimers. Experimental and theoretical results for dimers containing He, Ne, Ar, Kr and Xe are reviewed. These dimers are bound by London dispersive forces, which is one component of the van der Waals or intermolecular forces. Though these are usually called van der Waals complexes or van der Waals molecules, these dimers may be more appropriately called London molecules. Helium dimer is a particularly interesting case with the equilibrium internuclear distance estimated to be about 50 Angstrom

Molecule matters van der Waals molecules: 3 - Rg•••HF complexes are Debye molecules!

In this article, Debye's contributions to understanding van der Waals attractive forces, specifically, dipole-induced dipole interaction, is discussed. The Rg•••••••••HF complex structure is influenced by this interaction. Hence, these types of van der Waals molecules can be more specifically called Debye molecules

Peter debye

"Not to despair and always be ready to grab the Good which whisks by, without granting the Bad any more room than is absolutely necessary. That is a principle of which I have already made much use. Hopefully, the new year will bring more good than our little faith allows us to see at this moment.

C5H9N Isomers: Pointers to Possible Branched Chain Interstellar Molecules

The astronomical observation of isopropyl cyanide further stresses the link between the chemical composition of the ISM and molecular composition of the meteorites in which there is a dominance of branched chain amino acids as compared to the straight. However, observations of more branched chain molecules in ISM will firmly establish this link. In the light of this, we have considered C5H9N isomeric group in which the next higher member of the alkyl cyanide and other branched chain isomers belong. High-level quantum chemical calculations have been employed in estimating accurate energies of these isomers. From the results, the only isomer of the group that has been astronomically searched, n-butyl cyanide is not the most stable isomer and therefore, which might explain why its search could only yield upper limits of its column density without a successful detection. Rather, the two most stable isomers of the group are the branched chain isomers, tert-butylnitrile and isobutyl cyanide. Based on the rotational constants of these isomers, it is found that the expected intensity of tert-butylnitrile is the maximum among this isomeric group. Thus, this is proposed as the most probable candidate for astronomical observation. A simple LTE (Local thermodynamic equilibrium) modelling has also been carried out to check the possibility of detecting tert-butyl cyanide in the millimetre-wave region.Comment: 16 pages, 1 figur

The hydrogen bond: a molecular beam microwave spectroscopist's view with a universal appeal

In this manuscript, we propose a criterion for a weakly bound complex formed in a supersonic beam to be characterized as a 'hydrogen bonded complex'. For a 'hydrogen bonded complex', the zero point energy along any large amplitude vibrational coordinate that destroys the orientational preference for the hydrogen bond should be significantly below the barrier along that coordinate so that there is at least one bound level. These are vibrational modes that do not lead to the breakdown of the complex as a whole. If the zero point level is higher than the barrier, the 'hydrogen bond' would not be able to stabilize the orientation which favors it and it is no longer sensible to characterize a complex as hydrogen bonded. Four complexes, Ar2-H2O, Ar2-H2S, C2H4-H2O and C2H4-H2S, were chosen for investigations. Zero point energies and barriers for large amplitude motions were calculated at a reasonable level of calculation, MP2(full)/aug-cc-pVTZ, for all these complexes. Atoms in molecules (AIM) theoretical analyses of these complexes were carried out as well. All these complexes would be considered hydrogen bonded according to the AIM theoretical criteria suggested by Koch and Popelier for C-H···O hydrogen bonds (U. Koch and P. L. A. Popelier, J. Phys. Chem., 1995, 99, 9747), which has been widely and, at times, incorrectly used for all types of contacts involving H. It is shown that, according to the criterion proposed here, the Ar2-H2O/H2S complexes are not hydrogen bonded even at zero kelvin and C2H4-H2O/H2S complexes are. This analysis can naturally be extended to all temperatures. It can explain the recent experimental observations on crystal structures of H2S at various conditions and the crossed beam scattering studies on rare gases with H2O and H2S

Autocatalysis - a misnomer?

This article does not have an abstract

One hundred years of Lewis Chemical Bond!

This article does not have an abstract

Infrared spectra of dimethylnaphthalenes in the gas phase

We report the infrared spectra at 0.5 cm-1 resolution of three dimethylnaphthalenes (DMNs), namely 1,5-DMN, 1,6-DMN and 2,6-DMN in the gas phase at an elevated temperature recorded with the help of a variable path-length cell. DFT calculations have been carried out at B3LYP levels of theory with 6-31G as basis set to determine the harmonic frequencies and intensities of the DMNs to assign the experimentally observed spectra. We have compared the experimentally observed and theoretically calculated spectra of the dimethylnaphthalenes and assignments have been made. The observed and predicted frequencies and relative intensities are generally in good agreement. The intense aromatic C-H out-of-plane bending vibration observed around 800 cm-1 and three methyl C-H symmetric and asymmetric stretching vibrations around 2900 cm-1 have been recognized as unique bands to identify various DMNs in a mixture. The high-resolution IR spectroscopy of these three important polycyclic aromatic hydrocarbons which are present in the atmosphere have been discussed

Infrared chemiluminescence studies of H + BrCN and H abstraction by CN reactions. Importance of the HNC channel

The H + BrCN reaction and the H abstraction reactions from HI, H2S, PH3, SiH4, CH3OCH3, c-C5H10 and C(CH3)4 by CN were studied by infrared chemiluminescence in a fast flow reactor. From the dependence of the HCN and HNC emission intensities on temperature, activation energies of 5.2 ± 0.4 and 7.5 ± 0.8 kcal mol-1 were assigned for the HCN and HNC channels from the H + BrCN reaction. The anharmonicity constant, X3,3 for HNC, was determined to be 66 cm-1. All reactions yielded HCN with an inverted vibrational distribution in v2 along with v2 excitation and <fv> = 0.4-0.5. The abstraction reaction PH3 and HI produced HNC (v3,≥ 1) with HNC/HCN ratios of ≥ 0.02 and ≥ 0.43, respectively