The 1-v″ bands progression of the BΣ → XΣ system of CO

The B²Σ⁺ → X²Σ⁺ (0-1, 2, 3, 4 progression) electronic transition of ¹²C¹⁷O⁺ was first observed and analyzed by Szajna and Ke¸pa [Spectrochim. Acta A 65 (2006) 1014-1020]. We have now extended our previous studies. The use of high resolution conventional spectroscopic techniques has allowed first rotational analysis of the 1-2, 1-3, 1-4 and 1-5 bands of the first negative system in the 37,000-43,000 cm⁻¹ spectral region. Approximately 500 transition wavenumbers were measured with an estimated accuracy of 0.005 cm⁻¹. The present data were combined with the previous measurements to yield an improved set of molecular constants for the B²Σ⁺(v′ = 0, 1) and X²Σ⁺(v″ = 1, 2, 3, 4, 5). The v′ = 1 and v″ = 5 vibrational levels were observed for the first time and the main molecular constants are (in cm⁻¹, one standard deviation in parentheses)

B2Σ+		X2Σ+
B1 = 1.710792(20)		B5 = 1.825694(23)
D1 = 7.799(15) × 10−6		D5 = 6.085(21) × 10−6
γ1 = 1.9491(37) × 10−2		γ5 = [8.381] × 10−3

Full-size table

     

Spectroscopy of AlO: Combined analysis of the AΠi → XΣ and BΣ → XΣ transitions

A combined analysis of the A²Π_i → X²Σ⁺ and B²Σ⁺ → X²Σ⁺ band systems of AlO, involving 21,500 line assignments, has been performed. The analysis indicates that the previously reported γ values of the B²Σ⁺ state are questionable. The present analysis shows that γ(B²Σ⁺) ≈ 0.014 cm⁻¹, essentially independent of the vibrational level. The positive sign is consistent with second order interaction with the higher-lying C²Π_r and lower-lying A²Π_i states. It also appears that many of the previously reported γ and γ_D values of X²Σ⁺ (v > 0) are doubtful. In fact, γ(X²Σ⁺) is observed to become increasingly negative for v″ > 1, due to second order interaction with the low-lying A²Π_i state. The present results are based on models where the hyperfine structure of the ²Σ⁺ states has been taken into account explicitly. Intensity patterns of the branches of the B²Σ⁺ → X²Σ⁺ system have been shown to be influenced by the case bβ_S coupling in the ground state v = 0,1 levels. This gives rise to intensity differences of around 10 percent in the R₁/R₂ and P₁/P₂ doublet components. The synthesized intensity patterns are fully in accord with the F₁/F₂ assignments of the present work.     

Rotational analysis of the (3, 6) band in the comet-tail (AΠi -XΣ) system of CO

The direct observation and rotational analysis of the (3, 6) band in the comet-tail (A²Π_i-X²Σ⁺) system of CO⁺ are carried out for the first time employing optical heterodyne and magnetic rotation enhanced velocity modulation spectroscopy. That 193 lines are assigned to this band ranging from 12 100 to 12 370 cm⁻¹ results in most accurate molecular constants by nonlinear least-squares fitting procedure employing the effective Hamiltonians.     

Sub-Doppler laser absorption spectroscopy of the AΠi − XΣ (1, 0) band of CN: Measurement of the N hyperfine parameters in AΠ CN

Measurements of multiple rotational lines in the (1, 0) band of the A²Π_i − X²Σ⁺ “red” system of the cyanogen radical (CN) at sub-Doppler resolution are reported. The CN radical was produced by 193 nm photodissociation of NCCN (ethane dinitrile) and detected with a Ti:sapphire ring laser operating near 10 900 cm⁻¹. The sample was exposed to a weak, frequency-modulated probe beam and a strong, counterpropagating bleach laser beam. Demodulated probe laser signals display absorption and dispersion features derived from Doppler-free saturation of the hyperfine components as the laser scans across the central region of a Doppler-broadened rotational line spectrum. Hyperfine-resolved transition frequencies were combined with known ground-state X²Σ hyperfine term values to determine A²Π state hyperfine term values, which were analyzed in terms of an effective Hamiltonian for the A²Π state. All the expected hyperfine and ¹⁴N quadrupolar parameters were determined and their values analyzed in terms of a simple molecular orbital picture of the bonding in the radical. Higher sensitivity obtained with 400 kHz amplitude modulation of the bleach laser and additional phase-sensitive detection allowed hyperfine splittings in some rotational lines of ¹³C¹⁴N to be observed in natural abundance. Excited state hyperfine splittings were determined for a selection of rotational states, but not enough to determine the ¹³C hyperfine parameters.     

Doppler-limited spectroscopy of the AΠ1 ← XΣ system of ICl in the 0.8 μm region using a Ti:sapphire ring laser

Doppler-limited vib-rotational absorption spectra of the A ← X electronic transition of I^35/37Cl are measured in the range 11,352-13,507 cm⁻¹ using a Ti:sapphire ring laser. The P-, Q-, and R-branch lines belonging to the v ← v″ = (0-7) ← (0-7) transition in I³⁵Cl and the v ← v″ = (0-6) ← (2-6) transition in I³⁷Cl are assigned. Under Doppler-limited conditions, the P- and R-branch lines are split into doublets by the nuclear quadrupole coupling effect of the I atom. The unperturbed positions of these lines are correctly calculated, whereas splitting in the Q-branch lines was not observed. The mass-reduced Dunham expansion coefficients U_l,m of the A and X states and the spectroscopic constants , and H_v^′ of the A state are determined using a global least-squares fitting procedure.     

Rotational analysis of weak (4, 6) hot band in the comet-tail (AΠi-XΣ) system of the CO

The ro-vibrational spectrum of the weak (4, 6) hot band in the comet-tail (A²Π_i-X²Σ⁺) system of CO⁺ is observed by employing optical heterodyne and magnetic rotation enhanced velocity modulation spectroscopy. One hundred and twenty-four spectral lines are assigned to this band; thus, precise molecular constants of the levels involved are obtained from a weighted nonlinear least-squares fitting procedure combining with our previous spectrum of the (3, 6) band.     

Absorption spectrum of the (2, 1) band in the AПi-XΣ system of CS cation

The spectrum of CS⁺ cation was recorded in the 12,235-12,600 cm⁻¹ region by employing optical heterodyne velocity modulation absorption spectroscopy. In combination with simultaneous measurement of optical heterodyne concentration modulation absorption spectroscopy, the spectral lines of CS⁺ blended with the neutral CS lines were identified and extracted from the observed spectra. One hundred and eighty-two spectral lines of CS⁺ were assigned to the (2, 1) band in the A²П_i-X²Σ⁺ system and the improved molecular constants of the upper level (υ = 2) in the A²П_i state were derived by nonlinear least squares fitting.     

Sub-millimeter spectroscopy of BaS (XΣ)

The pure rotational spectrum of BaS (X¹Σ⁺) has been recorded in the frequency range 355-396 GHz using direct absorption methods. Data were recorded for six isotopomers: ¹³⁸Ba³²S, ¹³⁷Ba³²S, ¹³⁶B³²S, ¹³⁵Ba³²S, ¹³⁴Ba³²S, and ¹³⁸Ba³⁴S, in vibrational states ranging from v = 0 to v = 6. This work is an extension of past microwave and millimeter studies. Revised spectroscopic constants have been established for the six species. The dissociation energy for ¹³⁸Ba³²S is estimated to be 42 392 cm⁻¹.     

Fourier transform spectroscopy of chemiluminescence from the AΠ-XΣ system of SrO

The A^′1Π-X¹Σ⁺ near infrared system of strontium oxide (SrO) was observed at high spectral resolution by measuring the chemiluminescence from a Broida flow reactor using a Fourier transform spectrometer. In total, 32 bands from , , were measured within the spectral region at a resolution of . Vibrational levels of the upper state were observed up to v_A^′=4, and more than 5600 rotational lines were assigned. Incorporating previously published high resolution data for the A¹Σ⁺-X¹Σ⁺ system, a global fit to both data sets yields improved Dunham constants for the ground state and for the lower vibrational levels (v_A^′=0, 1, and 2) of the A^′1Π state. Because perturbations arising from interactions with the b³Σ⁺ and A¹Σ⁺ states affect the higher vibrational levels of the A^′1Π state more strongly, levels v_A^′=3 and 4 were represented by effective band constants in the fits. RKR potentials for the X¹Σ⁺,A^′1Π, and b³Σ⁺ states have been generated utilizing all the available data, Franck-Condon factors have been calculated for the A^′1Π-X¹Σ⁺ system, and A^′1Π∼b³Σ⁺ and A^′1Π∼A¹Σ⁺ perturbations are discussed.     

High-resolution Fourier transform emission spectroscopy of the AΠ-XΣ system of GeSe

Natural germanium and selenium consist of, respectively, five and six stable isotopes. Several of these isotopes have considerable abundances and one should expect to observe the bands of at least six isotopic variants of germanium monoselenide (GeSe). In this paper, for the first time, the results of the high-resolution electronic spectrum of the main transition A¹Π-X¹Σ⁺ of the specific isotopomer ⁷⁴Ge⁸⁰Se, excited in a microwave discharge and recorded in the 33 500-26 000 cm⁻¹ region using a Fourier transform spectrometer, is discussed. From the rotational analysis of 25 bands involving v″ = 0-12 and v′ = 0-7, accurate vibrational and rotational constants of the A¹Π state are determined. The present study has revealed perturbations in the v′ = 6 and 7 levels of the A¹Π state.     

Rotationally Resolved LIF Spectra of the AΣ-XΠr Transition of Jet-Cooled GeCl

The A²Σ⁺-X²Π_r band system of ⁷⁴Ge³⁵Cl has been rotationally resolved for the first time using isotopically enriched ⁷⁴GeCl₄ as the precursor in a pulsed discharge jet experiment. The previous vibrational analysis of W. J. Balfour and K. S. Chandrasekhar (1986, J. Phys. B19, L187-L191) has been verified from the observed isotopic splittings of both the chlorine and germanium isotopomers. The ²Π_1/2 components of three vibronic bands have been rotationally analyzed leading to revised values for the ground state rotational constant B″₀=0.154165(35) cm⁻¹ and the lambda-doubling constant p″₀=6.560(97)×10⁻³ cm⁻¹. We have experimentally determined the value of B′_e=0.118710(24) cm⁻¹ for the A²Σ⁺ state leading to an excited state equilibrium bond length of 2.44581(25) Å.     

NaK bound-free and bound-bound 4 Σ → aΣ emission

The relative transition dipole moment function M(R) for the 4 ³Σ⁺ → a³Σ⁺ electronic transition in the sodium-potassium molecule (NaK) has been determined by fitting experimental bound-free and bound-bound emission spectra. The fit is performed using a modified version of the BCONT computer program, which was originally developed by Le Roy. Spectra previously measured in this laboratory from low-lying ro-vibrational levels of the 4 ³Σ⁺ state and new spectra from high-lying levels are included in the fit. A slight adjustment to the inner, repulsive wall of the 4 ³Σ⁺ potential leads to an improved form for that curve. The fitted M(R), when appropriately scaled, agrees very well with recent ab initio calculations of Magnier et al.     

High-resolution Fourier-transform study of the X2Π3/2 → X1Π1/2 fine structure transitions of PbH and PbD

Near-infrared emission spectra of the X₂²Π_3/2 → X₁²Π_1/2 fine structure transitions of PbH and PbD have been investigated by high-resolution Fourier-transform spectrometry. The fine structure splitting in the X²Π_r ground state of ²⁰⁸PbH was found to be 6924.4926(4) cm⁻¹. Accurate rotational constants for the v = 0 and 1 vibrational levels of the X²Π_r states of ²⁰⁸PbH, ²⁰⁷PbH, ²⁰⁸PbD and ²⁰⁷PbD and hyperfine structure constants for the X₁²Π_1/2 states of ²⁰⁷PbH (²⁰⁷PbD) have been derived.     

Perturbations in the A1Π-X1Σ+ system of the BeO molecule

All perturbations observed by Lagerqvist (Thesis, University of Stockholm, 1948) in the A¹Π-X¹Σ⁺ transition have been assigned to a³Π₂, a³Π₁, and X¹Σ⁺ states. Vibrational and rotational constants of the a³Π state as well as electronic parameters for A ～ X, A ～ a, and a ～ X interactions have been determined.

     

16.

The far-infrared and microwave spectra of the CH radical in the v = 1 level of the XΠ state     

Michael Jackson  Lyndon R. Zink  Luis Perez 《Journal of Molecular Spectroscopy》2008,247(2):128-139

Transitions between the spin-rotational levels of the ¹²CH radical in the v = 1 level of the X²Π state have been studied by the technique of laser magnetic resonance at far-infrared wavelengths. The data have been combined with a measurement of lambda-doubling transition frequencies at 7 GHz to determine an improved set of molecular parameters for CH in the v = 1 level. The parameters provide information on the effects of vibrational excitation on the structural properties of CH. Accurate predictions of the transition frequencies between the low-lying levels of the radical in the absence of a magnetic field have also been made.Small inconsistencies in the least-squares fit of the laser magnetic resonance data prompted re-measurement of three far-infrared laser frequencies, the 122.5 μm line of CH₂F₂ pumped by 9R(22), the 122.5 μm line of CH₂F₂ pumped by 9P(8) and the 554.4 μm line of CH₂CF₂ pumped by 10P(14). The new measurements differ by as much as 3.8 MHz from those made previously and are more accurate; they also remove the inconsistencies in the fit. The re-measured frequencies of the two 122.5 μm lines are identical within experimental error which suggests that the far-infrared lasing transition is the same, namely the ^rR₂₃(32) transition in the v₉=1 level of CH₂F₂.     

17.

Photoemission from α and β phases of the GaAs(0 0 1)-c(4 × 4) surface     

P. Ji?í?ek  M. Cukr  J. Sadowski 《Surface science》2009,603(20):3088-3093

We prepared α- and β surface phases of GaAs(0 0 1)-c(4 × 4) reconstruction by molecular beam epitaxy (MBE) using As₄ and As₂ molecular beams, respectively, and examined them by angle-resolved ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS) with synchrotron radiation as an excitation source. The UPS valence band spectra and the XPS 3d core level data show pronounced differences corresponding to the surface composition and the atomic structure of the two phases, as proposed in the literature. In UPS, the β phase is characterized by an intensive surface state 0.5 eV below the top of the valence band at low photon energy, while an analogous peak in the α phase spectra is missing. The surface state is interpreted in terms of dangling bonds on As dimers. The As3d and Ga3d core level photoelectron lines exhibit phase-specific shapes as well as differences in the number, position and intensity of their deconvoluted components. The location of various atoms in the surface and subsurface layers is discussed; our photoemission results support models of the β phase and the α phase with As-As dimers and Ga-As heterodimers, respectively.     

18.

The A²Π-X²Π system of the SbO molecule     

Walter J Balfour  Ram S Ram 《Journal of Molecular Spectroscopy》1984,105(1):246-259

The emission spectrum of the A²Π-X²Π system of the SbO molecule has been photographed under high resolution, and the rotational structure in eight bands of the ${}^2\text{Π}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{-}{}^2\text{Π}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ component, involving v′ = 0–2 and v″ = 1–4, has been analyzed for both isotopic molecules ¹²¹SbO and ¹²³SbO. The observed rotational lines of the corresponding ${}^2\text{Π}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{-}{}^2\text{Π}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ component are broad, with a width of about 0.2 cm^?1 varying little with J. It is suggested that these broad lines represent unresolved components arising from magnetic hyperfine interaction with ¹²¹Sb or ¹²³Sb nuclei. Isotopic shift observations contradict earlier vibrational assignments in the ${}^2\text{Π}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{-}{}^2\text{Π}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ subsystem and indicate that the A state is inverted in agreement with expectations from related systems. The principal molecular constants (in cm^?1) obtained for ¹²¹SbO are

	Reciprocal centimeters
	Te	ωe	ωexe	Be	αe	re (Å)
a3Π	8574	1132	8.4	1.3675	?0.0168	1.4623

     

19.

Pinning-depinning behavior in the wetting of (0 0 0 1) α-Al₂O₃ single crystal by molten Mg     

Laixin ShiPing Shen  Dan ZhangQichuan Jiang 《Applied Surface Science》2011,257(24):10743-10747

Wetting of (0 0 0 1) α-Al₂O₃ single crystal by molten Mg was studied by an improved sessile drop method in a purified flowing Ar atmosphere. A distinct pinning-depinning behavior was observed during the evaporation-coupled wetting process. The underlying mechanism for this behavior was expatiated from the viewpoints of energetics and geometries at the triple junction.     

20.

High sensitivity CRDS of the aΔ_g−XΣ_g band of oxygen near 1.27 μm: Extended observations, quadrupole transitions, hot bands and minor isotopologues     

Olga Leshchishina  Samir Kassi  Laurence S. Rothman  Alain Campargue 《Journal of Quantitative Spectroscopy & Radiative Transfer》2010,111(15):2236-2245

The CW-Cavity Ring Down Spectroscopy (CW-CRDS) technique has been used to record the high sensitivity absorption spectrum of the a¹Δ_g-X³Σ_g⁻ band of oxygen near 1.27 μm. The spectra were obtained between 7640 and 7917 cm⁻¹ with “natural” oxygen and with a sample highly enriched in ¹⁸O. The absolute intensities of 376 and 643 oxygen transitions were measured in the two spectra. They include the a¹Δ_g−X³Σ_g⁻ (0-0) bands of ¹⁶O₂, ¹⁶O¹⁸O, ¹⁶O¹⁷O, ¹⁷O¹⁸O and ¹⁸O₂. The (0-0) bands of ¹⁶O₂ and ¹⁸O₂ show weak quadrupole transitions with line intensities ranging from 1×10⁻³⁰ to 1.9×10⁻²⁸ cm/molecule. They are accompanied by the a¹Δ_g−X³Σ_g⁻ (1-1) hot bands, which are reported for the first time. The line profiles of the transitions of the ¹⁶O¹⁷O and ¹⁷O¹⁸O isotopologues were observed to be broadened due to an unresolved magnetic hyperfine structure. Accurate spectroscopic parameters of the different energy levels involved in the observed bands were derived from a global fit of the observed line positions, combined with microwave and Raman measurements available in the literature.     

State	$\text{T}{}_{\mathrm{e}}$	$\text{ω}{}_{\mathrm{e}}$	$\text{ω}{}_{\mathrm{e}}\text{χ}{}_{\mathrm{e}}$	$\text{B}{}_{\mathrm{e}}$	$\text{10}{}^3\text{α}{}_{\mathrm{e}}$	$\text{10}{}^7\text{D}{}_{\mathrm{e}}$
$\text{X}{}^2\text{Π}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$	0	818.7	4.2	—	—	—
$\text{X}{}^2\text{Π}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$	x ≈ 2272	814.1	4.3	0.35920	2.38	2.8
$\text{A}{}^2\text{Π}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$	21 467.4	565.8	2.9	—	—	—
$\text{A}{}^2\text{Π}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$	x + 18 521.7	570.4	2.6	0.28856	1.82	2.9

The far-infrared and microwave spectra of the CH radical in the v = 1 level of the XΠ state

Transitions between the spin-rotational levels of the ¹²CH radical in the v = 1 level of the X²Π state have been studied by the technique of laser magnetic resonance at far-infrared wavelengths. The data have been combined with a measurement of lambda-doubling transition frequencies at 7 GHz to determine an improved set of molecular parameters for CH in the v = 1 level. The parameters provide information on the effects of vibrational excitation on the structural properties of CH. Accurate predictions of the transition frequencies between the low-lying levels of the radical in the absence of a magnetic field have also been made.Small inconsistencies in the least-squares fit of the laser magnetic resonance data prompted re-measurement of three far-infrared laser frequencies, the 122.5 μm line of CH₂F₂ pumped by 9R(22), the 122.5 μm line of CH₂F₂ pumped by 9P(8) and the 554.4 μm line of CH₂CF₂ pumped by 10P(14). The new measurements differ by as much as 3.8 MHz from those made previously and are more accurate; they also remove the inconsistencies in the fit. The re-measured frequencies of the two 122.5 μm lines are identical within experimental error which suggests that the far-infrared lasing transition is the same, namely the ^rR₂₃(32) transition in the v₉=1 level of CH₂F₂.     

Photoemission from α and β phases of the GaAs(0 0 1)-c(4 × 4) surface

We prepared α- and β surface phases of GaAs(0 0 1)-c(4 × 4) reconstruction by molecular beam epitaxy (MBE) using As₄ and As₂ molecular beams, respectively, and examined them by angle-resolved ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS) with synchrotron radiation as an excitation source. The UPS valence band spectra and the XPS 3d core level data show pronounced differences corresponding to the surface composition and the atomic structure of the two phases, as proposed in the literature. In UPS, the β phase is characterized by an intensive surface state 0.5 eV below the top of the valence band at low photon energy, while an analogous peak in the α phase spectra is missing. The surface state is interpreted in terms of dangling bonds on As dimers. The As3d and Ga3d core level photoelectron lines exhibit phase-specific shapes as well as differences in the number, position and intensity of their deconvoluted components. The location of various atoms in the surface and subsurface layers is discussed; our photoemission results support models of the β phase and the α phase with As-As dimers and Ga-As heterodimers, respectively.     

The A2Π-X2Π system of the SbO molecule

The emission spectrum of the A²Π-X²Π system of the SbO molecule has been photographed under high resolution, and the rotational structure in eight bands of the ${}^2\text{Π}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{-}{}^2\text{Π}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ component, involving v′ = 0–2 and v″ = 1–4, has been analyzed for both isotopic molecules ¹²¹SbO and ¹²³SbO. The observed rotational lines of the corresponding ${}^2\text{Π}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{-}{}^2\text{Π}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ component are broad, with a width of about 0.2 cm^?1 varying little with J. It is suggested that these broad lines represent unresolved components arising from magnetic hyperfine interaction with ¹²¹Sb or ¹²³Sb nuclei. Isotopic shift observations contradict earlier vibrational assignments in the ${}^2\text{Π}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{-}{}^2\text{Π}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ subsystem and indicate that the A state is inverted in agreement with expectations from related systems. The principal molecular constants (in cm^?1) obtained for ¹²¹SbO are

Pinning-depinning behavior in the wetting of (0 0 0 1) α-Al2O3 single crystal by molten Mg

Wetting of (0 0 0 1) α-Al₂O₃ single crystal by molten Mg was studied by an improved sessile drop method in a purified flowing Ar atmosphere. A distinct pinning-depinning behavior was observed during the evaporation-coupled wetting process. The underlying mechanism for this behavior was expatiated from the viewpoints of energetics and geometries at the triple junction.     

High sensitivity CRDS of the aΔg−XΣg band of oxygen near 1.27 μm: Extended observations, quadrupole transitions, hot bands and minor isotopologues

The CW-Cavity Ring Down Spectroscopy (CW-CRDS) technique has been used to record the high sensitivity absorption spectrum of the a¹Δ_g-X³Σ_g⁻ band of oxygen near 1.27 μm. The spectra were obtained between 7640 and 7917 cm⁻¹ with “natural” oxygen and with a sample highly enriched in ¹⁸O. The absolute intensities of 376 and 643 oxygen transitions were measured in the two spectra. They include the a¹Δ_g−X³Σ_g⁻ (0-0) bands of ¹⁶O₂, ¹⁶O¹⁸O, ¹⁶O¹⁷O, ¹⁷O¹⁸O and ¹⁸O₂. The (0-0) bands of ¹⁶O₂ and ¹⁸O₂ show weak quadrupole transitions with line intensities ranging from 1×10⁻³⁰ to 1.9×10⁻²⁸ cm/molecule. They are accompanied by the a¹Δ_g−X³Σ_g⁻ (1-1) hot bands, which are reported for the first time. The line profiles of the transitions of the ¹⁶O¹⁷O and ¹⁷O¹⁸O isotopologues were observed to be broadened due to an unresolved magnetic hyperfine structure. Accurate spectroscopic parameters of the different energy levels involved in the observed bands were derived from a global fit of the observed line positions, combined with microwave and Raman measurements available in the literature.