Reactive intermediates in 4He nanodroplets: Infrared laser Stark spectroscopy of dihydroxycarbene

Abstract

Singlet dihydroxycarbene (HOC̈OH) is produced via pyrolytic decomposition of oxalic acid, captured by helium nanodroplets, and probed with infrared laser Stark spectroscopy. Rovibrational bands in the OH stretch region are assigned to either trans,trans- or trans,cis-rotamers on the basis of symmetry type, nuclear spin statistical weights, and comparisons to electronic structure theory calculations. Stark spectroscopy provides the inertial components of the permanent electric dipole moments for these rotamers. The dipole components for trans, trans- and trans, cis-rotamers are (μa, μb) = (0.00, 0.68(6)) and (1.63(3), 1.50(5)), respectively. The infrared spectra lack evidence for the higher energy cis,cis-rotamer, which is consistent with a previously proposed pyrolytic decomposition mechanism of oxalic acid and computations of HOC̈OH torsional interconversion and tautomerization barriers.

Infrared spectroscopy in superfluid helium droplets

“…than the energy of the thermally populated rotational states, so free rotation is replaced by libration of molecules around the electric field, which is described by motion in a parabolic potential [164,173,174]. The Stark spectra get more complex for open shell molecules, such as radicals [60,162,163,175,176]. One such example is that of hydroxyl radical (OH) which shows Ʌ-doubling of the Q(3/2) rotational branch [155].…”

“…Electric field study in helium droplets have also been employed for structure determination of molecular complexes, such as (HF) n [127], (H 2 O) m -(HCl) n [130], H 2 O clusters [187], and others [183,184,188]. VTMA was also instrumental in determination of the structure and spectral assignment of pre-reactive complexes [162,163,175,176,178].…”

Interaction of N‐Heterocyclic Carbenes and Simple Carbenes with Small Molecules (One to Three Atoms) Excluding Metals: Formation of Covalent C–X Bonds

“…These reactions have been reported several times [75], for instance by Sander et al [76] and by Tkatchenko et al [77]. The reaction of dihydroxycarbene, HOC(:)OH, with CO 2 has been studied by infrared laser Stark spectroscopy [78].…”

“…. The reaction of dihydroxycarbene, HOC( : )OH, with CO 2 has been studied by infrared laser Stark spectroscopy . Note that structures 22 and 23 involve the weak CC interaction named “tetrel bond” .…”

Infrared laser Stark spectroscopy of hydroxymethoxycarbene in 4He nanodroplets

“…Isomerization rates for this class of reactive intermediates are largely dictated by the R and R substituent groups [17]. For example,dihydroxycarbene (HOC OH) shows no propensity for tunneling on any practical experimental timescale, as recently demonstrated in Ar matrix isolation studies [18].Recent gas-phase and He nanodroplet spectroscopic studies with theoretical calculations have structurally characterized HOC OH [19,20]. The back-donated electron density from the second O atom into the empty C atomp-orbital of HOC OH plays a significant role in its stability towards tunneling, in comparison to the analogous HC OH and CH 3 C OH systems, which undergorelatively prompt isomerization [15,16,21].…”