Determination of precise relative energies of conformers of n-propanol by rotational spectroscopy

Abstract

The rotational spectrum of n-propanol (n-CH(3)CH(2)CH(2)OH) was studied with several techniques of contemporary broadband rotational spectroscopy at frequencies from 8 to 550 GHz. Rotational transitions in all five conformers of the molecule, Gt, Gg, Gg', Tt, and Tg, have been unambiguously assigned. Over 6700 lines of the Gt, Gg, and Gg' species, for quantum number values reaching K(a) = 33 and J = 67, were fitted in a joint analysis leading to the determination of DeltaE(Gg-Gt) = 47.82425(25) cm(-1) and DeltaE (Gg'-Gg) = 3.035047(11) cm(-1). Stark effect measurements in supersonic expansion were used to further confirm the assignment. The results are compared with those for the ethanol molecule and with ab initio calculations, allowing several inferences to be drawn concerning the differences in the large amplitude torsional potential of the hydroxyl group in the two molecules.

Exploring molecular complexity with ALMA (EMoCA): Alkanethiols and alkanols in Sagittarius B2(N2)

“…Orientations of the methyl group are designated by upper-case characters, those of the OH group by lower-case characters. The Ga conformer is lowest in energy, and the two non-equivalent Gg and Gg' conformers are higher by 68.81 K and 73.17 K, respectively, as determined from perturbations in rotational transitions of Ga at high K a quantum numbers and from perturbations between Gg and Gg' (Kisiel et al 2010). The energy of the Aa conformer relative to Ga is known only approximately, but it appears to be lower than that of either Gg and Gg' (Kahn & Bruice 2005).…”

“…These transitions all have rather high values of K a and will be of importance for astronomical observations only if lower energy transitions have been detected with very high signal-to-noise ratios and at high rotational temperatures. Dipole moment components of µ a = 0.4914 (4) D, µ b = 0.9705 (13) D, and µ c = 0.9042 (12) D were determined by Kisiel et al (2010) from a single state fit. Based on the relative energies of the npropanol conformers, their total column density in the ground vibrational state at 150 K is about a factor of 3.3 higher than that determined for the Ga conformer; inclusion of thermal population of vibrational states (Fukushima & Zwolinski 1968) yields a combined factor of about 5.2.…”

Division Xii/Commission 14/Working Group on Molecular Data

“…The rotational spectrum of ethyl formate has also been revisited (Medvedev et al 2009). Other studies include cyclo-propyl cyanide (Bizzocchi et al 2008) and iso-propyl cyanide , two conformers of ethylene glycol (Christen & Müller 2003;Müller & Christen 2004), microwave spectra of several conformers of 1,2-and 1,3-propanediol Plusquellic et al 2009), propane , millimeter wave spectra of the amino acids glycine and alanine (Ilyushin et al 2005;Hirata et al 2008), acetamide (Ilyushin et al 2004), methylamine (Ilyushin & Lovas 2007), acetic acid (Ilyushin et al 2008), n-propanol (Kisiel et al 2010), and diethyl ether (Walters et al 2009). Other investigations may turn out to also be relevant once telescope arrays such as EVLA, NOEMA, or ALMA conduct large scale line surveys or dedicated seaches for particular molecules.…”

Infrared Photoisomerization of 1-Propanol CD3 and OD Trapped in Four Cryogenic Matrices: Ne, N2, Ar, and Xe

“…ABSTRACT: The conformational equilibria and isomerization processes of 1-propanol -OD and -CD 3 have been studied by vibrational spectroscopy at low temperatures in four cryogenic matrices to investigate the effect of deuteration on their photochemistry. These isotopic species were selectively irradiated in the ν OH and ν OD domains, resulting in the identification of several conformers that are able to interconvert upon selective IR irradiation.…”