We have investigated the effect of ice substrate on the temperature dependent structural changes of formic acid. Infrared spectra of HCOOH@KBr, HCOOH@H 2O amorphous and HCOOH@H 2O crystalline were measured in the temperature range of 18-180 K (X@Y represents X deposited on Y). At 18 K formic acid deposited over ice exists principally as its dimer. Upon increase of temperature, the dimer gets converted to the polymeric crystalline form. In the case of amorphous ice surface, this conversion starts at a lower temperature of 37 K. For KBr and crystalline ice surfaces, this occurs at 98 and 83 K, respectively. The dangling -OH found on amorphous ice surfaces disappears completely upon formic acid deposition. The greater mobility of formic acid molecules on amorphous ice aids in the early onset of its crystallization. © 2004 Elsevier B.V. All rights reserved.

Pradeep Thalappil

Department Of Chemistry

Formic acid

STRUCTURAL CHANGES

temperature dependence

ULTRA COLD ICE SURFACES

Crystallization

Dimers

infrared spectroscopy

molecular dynamics

Potassium compounds

Surfaces

Thermal effects

Carboxylic acids

crystallin

dimer

article

chemical structure

COLD TREATMENT

low temperature

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Chemical Physics Letters

Extremely surface specific information, limited to the first atomic layer of molecular surfaces, is essential to understand the chemistry and physics in upper atmospheric and interstellar environments. Ultra low energy ion scattering in the 1-10 eV window with mass selected ions can reveal extremely surface specific information which when coupled with reflection absorption infrared (RAIR) and temperature programmed desorption (TPD) spectroscopies, diverse chemical and physical properties of molecular species at surfaces could be derived. These experiments have to be performed at cryogenic temperatures and at ultra high vacuum conditions without the possibility of collisions of neutrals and background deposition in view of the poor ion intensities and consequent need for longer exposure times. Here we combine a highly optimized low energy ion optical system designed for such studies coupled with RAIR and TPD and its initial characterization. Despite the ultralow collision energies and long ion path lengths employed, the ion intensities at 1 eV have been significant to collect a scattered ion spectrum of 1000 counts/s for mass selected CH 2+. © 2014 AIP Publishing LLC.

Fulltext

Review of Scientific Instruments

Development of ultralow energy (1-10 eV) ion scattering spectrometry coupled with reflection absorption infrared spectroscopy and temperature programmed desorption for the investigation of molecular solids

A study was conducted to demonstrate low-energy ionic collisions at molecular solids. The investigations were limited to molecular surfaces and associated chemical processes occurring during impact of a hyperthermal energy ion. The term 'molecular solid' comprised the wide range of molecular materials that were used in ion/surface collision experiments. The energy regime considered in the investigations lied in an intermediate range. Primary ion energies of several kiloelectronvolts used in a secondary ion mass spectrometry (SIMS) experiment was considered in the case of condensed molecular solids to allow correlation with the results of chemical sputtering (CS) or other low-energy sputtering (LES) experiments.

Chemical Reviews

Low-energy ionic collisions at molecular solids

In this work, we have examined the diffusive mixing of chloromethanes in different molecular solids H2O, D2O, and CH3OH by monitoring their chemical sputtering spectra due to the impact of Ar + ions in the collision energy range of 3-60 eV, focusing on amorphous solid water. The chemical sputtering spectra have been monitored over the temperature window accessible by liquid nitrogen, and the coverages of the molecules of interest and ice have been varied from one to several hundred monolayers. Instrumentation and sensitivity of the technique have been discussed. It is found that while the diffusion of CCl4 in the molecular solids investigated is hindered, other choloromethanes such as CHCl3 and CH2Cl2 undergo diffusive mixing over the same temperature range. Quantitatively, while ∼4 monolayers (ML) of ice are found to block CCl4 diffusion, the numbers are ∼250 and ∼600 ML for CHCl3 and CH2Cl2, respectively. Crystallinity of ice does not have any effect on the diffusivity of water molecules when it is deposited below the chloromethanes. The effect of substrate was insignificant, and the rise in temperature increased diffusive mixing wherever the process was observed at a lower temperature. © 2007 American Chemical Society.

Journal of Physical Chemistry C

Probing difference in diffusivity of chloromethanes through water ice in the temperature range of 110-150 K

The concentration of carbon dioxide over melting ice oscillates was determined. A model that involved the melting of carbon dioxide containing ice, readsorption of vapor on ice and the dissolution in water was also proposed. The phenomena was observed over ice contaminated with salts or in the presence of nitrogen, and the oscillations were observed in many other solutes and ice water systems. The oscillatory behavior was found similar to carbon dioxide in all other solutes except in n-hexane, which is least soluble in water.

Physical Review Letters

Concentration of CO2 over melting ice oscillates

Hydrological Processes

Conference listing

The Journal of Chemical Physics

Infrared spectra oftrans-HOCO, HCOOH+, and HCO2− trapped in solid neon

Journal of Molecular Spectroscopy

Vibrational spectroscopy of cis- and trans-formic acid in solid argon

The Journal of Physical Chemistry A

Molecular Structure, Vibrational Frequencies, and Energetics of the HCO, HOCO, and HCO2Anions

Structural transformation in formic acid on ultra cold ice surfaces

Journal	Chemical Physics Letters
ISSN	00092614
Open Access	No