Detection of a higher energy isomer of the CO–N₂O van der Waals complex and determination of two of its intermolecular frequencies

Abstract

Infrared spectra in the carbon monoxide CO stretch region (∼2150 cm) and in the ν asymmetric stretch region of NO (∼2223 cm) are assigned to the previously unobserved O-bonded form of the CO-NO dimer ("isomer 2"). This van der Waals complex has a planar skewed T-shaped structure like that of the previously observed C-bonded form ("isomer 1"), but with the CO rotated by 180°. The effective intermolecular distance between the centers of mass is 3.51 Å for isomer 2 as compared to 3.88 Å for isomer 1. In addition to the fundamental band, two combination bands are observed for isomer 2, yielding values for two intermolecular vibrational modes: 14.502(5) cm for the coupled disrotatory motion or the uncoupled CO rock and 21.219(5) cm for the out-of-plane rock. We show that the published ab initio study on this system is inadequate in predicting the intermolecular frequencies for isomer 2 of CO-NO.

New Infrared Bands of the C-Bonded Isomer of OC–N2O and Determination of Two Intermolecular Frequencies

“…These authors predicted the existence of a second less-bonded isomer for CO–N 2 O and CO–CO 2 , the O-bonded form (isomer 2), similar to isomer 1 but with the CO unit rotated by 180°. These predictions were recently confirmed for CO–CO 2 and CO–N 2 O . The present work tests the quality of the ab initio intermolecular frequencies calculated in ref for isomer 1 of CO–N 2 O by comparing them with experimental values.…”

“…These predictions were recently confirmed for CO−CO 2 7 and CO−N 2 O. 8 The present work tests the quality of the ab initio intermolecular frequencies calculated in ref 6 for isomer 1 of CO−N 2 O by comparing them with experimental values. Furthermore, we are able to show that the value of the intermolecular frequency deduced from the two combination bands sharing the same intermolecular mode is insensitive to the nature of intramolecular excitation.…”

“…This is a hybrid a/b-type band dominated by b-type transitions. It has a similar structure to the lowest frequency combination band of isomer 2 observed at 2154.88 cm –1 , but stronger in intensity by a factor of 3 . The vibrational assignment for this band is most likely described as the in-plane CO-rock plus the CO stretch if the in-plane CO- and N 2 O-rock are uncoupled, or as the disrotatory bend plus the CO stretch if the CO- and N 2 O-rock are coupled .…”

Complex between Formic Acid and Nitrous Oxide: A Matrix-Isolation and Computational Study

“…Formic acid (HCOOH, FA) and nitrous oxide (N 2 O) participate in atmospheric chemistry. Formic acid is one of the major contributors to rainwater acidity in polluted and remote regions. , Nitrous oxide has a global warming potential nearly 300 times that of carbon dioxide and is one of the largest contributors to ozone depletion in the stratosphere. , Recent studies indicate that the FA and N 2 O annual emissions from known sources may have been significantly underestimated and suggest that these species might be more important to atmospheric chemistry than previously believed. , In addition, FA and N 2 O have been detected in interstellar molecular clouds and are relevant to studies of prebiotic species in astrochemistry. − The interest in noncovalent interactions of FA and N 2 O is considerable. − The formation of weakly bound complexes can cause changes in the stability and reactivity of the constituent monomers. − Quantum mechanical tunneling observed in FA is an exciting phenomenon that can affect the dynamics of the reactions and open new chemical reaction channels. , …”

How accurate is the determination of equilibrium structures for van der Waals complexes? The dimer N2O⋯CO as an example

“…The structure of N2O•••CO was first calculated at the MP2/6-311+G(d) level of theory by Venayagamoorthy and Ford. 22 Quite recently, the infrared spectrum of a higherenergy isomer was detected by Barclay et al 23 This isomer has a similar skewed T-shaped structure but with the CO rotated ca. 180°, suggesting a O•••N interaction.…”