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In this paper, we describe an experiment for the undergraduate physical chemistry laboratory in which students determine the speed of sound in the gases He, N[subscript 2], CO[subscript 2], and CF[subscript 3]CH[subscript 2]F. The experimental apparatus consists of a closed acrylic tube containing the gas under study. White audio noise is injected into one end of the tube, and the sound amplitude is recorded as a function of time at the other end. The data are recorded and Fourier transformed in real time with a spectrum analyzer application on an Apple iPad. The resulting frequency spectrum of the cavity standing waves is used to determine the speed of sound in the gas by least-squares fitting, with experimental values that fall within about 0.2% or less of the accepted values. The speed of sound is related to the heat capacity ratio in the ideal gas limit, providing students with quantitative evidence of the nonideality of the gases at ambient pressure and temperature. The experiment demonstrates the power and accuracy of interferometry and Fourier analysis using a modern tablet computer.

The D5Π–X5Δ (0,0) band of vanadium hydride at 654 nm has been recorded by laser excitation spectroscopy and represents the first analyzed spectrum of VH in the gas phase. The molecules were generated using a hollow cathode discharge source, with laser-induced fluorescence detected via the D5Π–A5Π (0,0) transition. All five main (ΔΩ = ΔΛ) subbands were observed as well as several satellite ones, which together create a rather complex and overlapped spectrum covering the region 15 180–15 500 cm−1. The D5Π state displays the effects of three strong local perturbations, which are likely caused by interactions with high vibrational levels of the B5Σ− and c3Σ− states, identified in a previous multiconfigurational self-consistent field study by Koseki et al. [J. Phys. Chem. A 108, 4707 (2004)]. Molecular constants describing the X5Δ, A5Π, and D5Π states were determined in three separate least-squares fits using effective Hamiltonians written in a Hund's case (a) basis. The fine structure of the ground state is found to be consistent with its assignment as a σπ2δ, 5Δ electronic state. The fitted values of its first-order spin–orbit and rotational constants in the ground state are A = 36.5378 15 c m − 1 and B = 5.7579(13) cm−1, the latter of which yields a bond length of R 0 = 1.7212 2 Å. This experimental value is in good agreement with previous computational studies of the molecule and fits well within the overall trend of decreasing bond length across the series of 3d transition metal monohydrides. [ABSTRACT FROM AUTHOR]

In this article, we describe an experiment for the undergraduate physical chemistry laboratory in which students measure the compressibility factor of two gases, helium and carbon dioxide, as a function of pressure at constant temperature. The experimental apparatus is relatively inexpensive to construct and is described and diagrammed in detail. Students analyze their data to determine values for the second virial coefficient for each gas, which may then be compared with the literature. The experiment demonstrates the nonideality of real gases. (Contains 2 tables and 2 figures.)

Here we describe an experiment for the undergraduate physical chemistry laboratory in which students synthesize the intermetallic compounds AlNi and AlNi3 and study them by X-ray diffractometry. The compounds are synthesized in a simple one-step reaction occurring in the solid state. Powder X-ray diffractograms are recorded for the two compounds as well as for the elements Al and Ni, all of which have cubic crystal structures. The students analyze the measured spectra to determine both the type of cubic lattice present and the unit cell dimension for comparison with the literature. The experiment demonstrates the utility of X-ray diffraction for structure determination.

We have recorded the A 2 Σ + − X 1 2 Π 3 / 2 (0,0) and B 2 Σ − − X 1 2 Π 3 / 2 (0,0) bands of gold monosulphide (AuS) at sub-Doppler resolution by intermodulated fluorescence spectroscopy. These two red-degraded bands lie at 642.3 and 613.8 nm, respectively. The high resolution of the experiment enabled the accurate determination of the rotational, fine and 197Au hyperfine constants of the two excited states for the first time. The Fermi contact dipolar and electric quadrupolar interactions in the upper states can be understood in terms of the electronic configurations from which they arise. The signs of the spin–rotation parameters, γ(A2Σ+) = −0.080821(24) cm−1 and γ(B2Σ−) = 0.136427(20) cm−1, suggest that the fine structures of these states arise primarily by interactions with inverted 2Π states lying at higher energy. [ABSTRACT FROM AUTHOR]

The B 2[uppercase_phi_synonym]5/2-X1 2Δ3/2(0,0) band at 778 nm and the C 2Δ3/2-X1 2Δ3/2(0,0) band at 737 nm of tantalum oxide (TaO) were recorded by laser excitation spectroscopy using a hollow cathode sputtering source to generate the molecules. The hyperfine structure arising from the 181Ta (I=7/2) nucleus was measured at sub-Doppler resolution using the technique of intermodulated fluorescence spectroscopy. The hyperfine structure was assigned and fitted in order to derive accurate values for the magnetic dipole and electric quadrupole interactions. The magnetic hyperfine constant for the ground electronic state was also calculated using the density functional theory as h3/2=625 MHz, in good agreement with the experimental value of 647±10 MHz. This result suggests that the X 2Δ ground state of TaO is well described by a pure δσ2 electronic configuration, where the unpaired electron is located in a Ta 5dδ orbital. [ABSTRACT FROM AUTHOR]

The laser excitation spectrum of the 327 nm band system of CoCl2, formed in a free-jet expansion, has been recorded at a rotational temperature of approximately 10 K. The spectrum is congested and suffers extensive perturbations. A progression in the excited state symmetric stretching vibration has been identified. The decrease in the symmetric stretching vibrational wave number on excitation is considerable [ν1′=195.7(12), ν1″=358.1(17) cm-1]. Despite widespread perturbations in the rotational structure of these vibronic bands, they can be confidently assigned to a parallel Ω=7/2-7/2 transition, consistent with an inverted 4Δg ground electronic state. The rotational constant for Co35Cl2 in the ground state is determined to be 0.056 65(11) cm-1, which corresponds to a value for the zero-point averaged Co–Cl bond length r0 of 2.062 8(40) Å. The perturbations are found to be strongly isotopomer dependent. [ABSTRACT FROM AUTHOR]

The spectrum associated with the J=3←2 transition of OH+ in the a 1Δ(v=0) state has been observed by far infrared laser magnetic resonance spectroscopy. A new microwave discharge source enabled the detection of this spectrum, which is the first observation of the rotational spectrum of an ion in a metastable state. Assignment and least-squares fitting of the observed transitions have determined the following molecular constants: B0=494.420 388 (22) GHz, the proton hyperfine parameter a=74.84 (32) MHz, gL’ = 1.000 915 (15), and gr=-0.001 815 (18), with the 1σ uncertainties of the last digits in parentheses. The relationship of these parameters to the geometric and electronic structure of OH+ is discussed. [ABSTRACT FROM AUTHOR]

We present a complete analysis of the hyperfine structure of the MnH A 7Π–X 7Σ+ (0,0) band near 5680 Å, studied with sub-Doppler resolution by intermodulated fluorescence spectroscopy. Magnetic hyperfine interactions involving both the 55Mn (I=5/2) and 1H (I=1/2) nuclear spins are observed as well as 55Mn electric quadrupole effects. The manganese Fermi contact interaction in the X 7Σ+ state is the dominant contributor to the observed hyperfine splittings; the ΔF=0, ΔN=0, ΔJ=±1 matrix elements of this interaction mix the electron spin components of the ground state quite strongly at low N, destroying the ‘‘goodness’’ of J as a quantum number and inducing rotationally forbidden, ΔJ=±2 and ±3 transitions. The hyperfine splittings of over 50 rotational transitions covering all 7 spin components of both states were analyzed and fitted by least squares, allowing the accurate determination of 14 different hyperfine parameters. Using single electronic configurations to describe the A 7Π and X 7Σ+ states and Herman–Skillman atomic radial wave functions to represent the molecular orbitals, we calculated a priori values for the 55Mn and 1H hyperfine parameters which agree closely with experiment. We show that the five high-spin coupled Mn 3d electrons do not contribute to the manganese hyperfine structure but are responsible for the observed proton magnetic dipolar couplings. Furthermore, the results suggest that the Mn 3d electrons are not significantly involved in bonding and demonstrate that the molecular hyperfine interactions may be quantitatively understood using simple physical interpretations. [ABSTRACT FROM AUTHOR]

Sub-Doppler spectra of the A 7Π–X 7Σ+ (0,0) band of gas phase MnH near 5680 Å were recorded by intermodulated fluorescence spectroscopy. The spectra reveal hyperfine splittings arising from both the 55Mn and 1H nuclear spins. Internal hyperfine perturbations have been observed between the different spin components of the ground state at low N‘. From a preliminary analysis of several rotational lines originating from the isolated and unperturbed F1(J‘=3) spin component of the X 7Σ+(N‘=0) level, the 55Mn Fermi contact interaction in the ground state has been measured as bF=Aiso =276(1) MHz. This value is 11% smaller than the value obtained by Weltner et al. from an electron-nuclear double resonance (ENDOR) study of MnH in an argon matrix at 4 K. This unprecedented gas-to-matrix shift in the Fermi contact parameter is discussed. [ABSTRACT FROM AUTHOR]

We have recorded the a4Σ−3/2 − X12Π3/2 (0,0), (1,0), and (2,0) bands of gaseous gold monosulphide (AuS) at sub-Doppler resolution in the near-infrared region. The molecules were made in a hollow cathode discharge source by the reaction of sputtered gold with carbonyl sulphide. The high resolution of the laser excitation spectrum enabled the determination of molecular constants describing the rotational and 197Au hyperfine structure in both states, as well as the spin-rotation interaction in the a4Σ−3/2 state. The natures of the two electronic states are discussed in the context of the observed hyperfine structure. [ABSTRACT FROM AUTHOR]