Improved measurements and analysis of the far-infrared spectrum of methanol-D1 (CH2DOH) arising from trans- (e0) to gauche- (e1 & o1) states

In this work the millimeter-wave (MMW) and far infrared (FIR) absorption spectrum for the asymmetrically deuterated Methanol (CH₂DOH) species measured recently at a temperature of −60 °C with better accuracy and signal/noise (S/N) ratio than known before has been assigned for transitions originating at the lowest lying trans- to gauche-states. The entire spectrum for 50–1200 cm⁻¹ has been re-recorded recently using the Synchrotron Radiation Source coupled with the Bruker Fourier Transform Infrared (FTIR) spectrometer with a resolution of about 0.001 cm⁻¹ or better. Complete spectrum has not been exploited a great deal but it helped to entangle overlapping lines in the present work. This also fills the gap remaining in the usual FTIR in the range 400–500 cm⁻¹. Hence it is expected to help the interacting partner for the Coriolis interaction encountered earlier. The assigned transitions mostly for the axial rotational angular momentum quantum number K + 1 ← K, both for R- and Q-sub bands for wide range of rotational angular momentum quantum number. The MMW spectrum has been recalibrated and assigned for a number of Q-branches. The assignments are confirmed rigorously using closed loop residual technique. The assigned ^rR and ^rQ lines have been analyzed in terms of polynomial expansion parameters. The new assignments are presented for about 750 transitions and a grand atlas of more than 1000 lines has been prepared which will be made available through the open source server at “research gate”. The present work should be useful in the area of astrophysical detection and further understanding of the energy relaxation pathways in the molecule.     

High resolution infrared spectrum of the CD2 wagging band of methanol-D2 (CHD2OH) for the lowest lying torsional vibrational state (e0)

This paper reports the analysis of the high resolution (0.0019 cm⁻¹) Fourier transform infrared (FTIR) spectrum for asymmetrically deuterated methanol CHD₂OH (methanol-D₂) at a low temperature for the CD₂ wagging band for the lowest lying trans-species (e₀). In spite of the complexity and perturbation in the spectra, assignments were possible for the CD₂ wagging band for a maximum K value of 10. In total, about 500 spectral lines have been assigned. Analysis of the spectral lines has been performed in terms of state dependent molecular parameters, Q-branch origins and asymmetry splitting. Assignments have been thoroughly confirmed using combination relations (see text). The catalogue of the assigned transition wavenumbers will help identification and prediction of far infrared (FIR) optically pumped CO₂ lasers. The absorption lines close to the several 10R and 10P CO₂ laser lines have also been identified. These should help experimentalists to optimize the power of the emission FIR laser lines and to predict new lines and should prove valuable as a laboratory support for interstellar detection in “Radio Astronomy”. To our knowledge this is the first time such vibrational infrared (IR) high resolution study in CHD₂OH is being performed.     

Fine structure of far infrared spectrum of ethanol in the lowest OH-torsional vibrational trans-state (e0) of ethanol

In this report the spectroscopic results for far infrared Fourier transform spectrum corresponding to the b-type transitions within the lowest lying trans-substrate (e₀) have been presented. The calculated matrix elements connecting various K-levels suggest that ΔK = 1 transitions within the trans- subs-state should be quite strong but the transitions between the trans state to the gauche states would quite week (practically non-existent). This was also concluded by previous studies using microwave and millimeter wave regions (Pearson et al., 1982; Millar, 1995). The assignments were confirmed by direct observations at the spectrum and the agreement between the observed and calculated spectrum using precise energy levels reported by Pearson et al. (1982). All the strong ^RR and some ^RQ branch lines starting from K = 10 ← 9 through K = 24 ← 23 have been identified. State dependent expansion parameters for all the 15 sub-bands have been presented. These parameters can reproduce the experimental wave numbers within experimental uncertainty. An atlas for about 450 transition lines corresponding to transitions within the e₀ torsional–vibrational species has been prepared. To our knowledge this is the first time the high resolution far infra-red spectral region study for ethanol have been performed.     

Fourier Transform Infrared spectrum of the OCD bending mode in methanol-D1

The infrared (IR) spectra corresponding to OCD bending vibration of asymmetrically deuterated methanol species CH₂DOH have been recorded with a Fourier Transform Spectrometer. The spectrum shows a typical structure of a parallel a-type band. This is expected because the bending vibration mainly executed parallel to the symmetry axis The Q-branch lines are grouped closely around 896 cm⁻¹ and the P- and R-Branches show complex structure. Nonetheless it was possible to assign a-type P- and R-branch lines up to K value of 8 and J value up to about 20 in most cases. The Q-branch lines for higher K values can be followed to about J = 15, the presence of which confirmed the assignments. The observations suggest that in the OCD bend some energy levels are highly interacted by highly excited torsional state from the ground torsional state. A full catalogue is presented along with the effective molecular parameters. An intensity anomaly was also observed in the transitions. So far it has been possible to assign only transitions between e₀ ← e₀ states. Plausible explanations of intensity anomaly are presented. Lastly, a number of optically pumped far infrared (FIR) laser lines have been assigned either to exact or tentative quantum states. These assignments should prove valuable for production of new FIR laser lines.     

Sub-millimeter wave spectroscopy of CHD2OH: a-type and asymmetry induced c-type transitions in the lowest three torsional sub-levels

The sub-millimeter wave (SMMW) spectral measurements using a fast scan backward wave oscillator based spectrometer have been carried out for asymmetrically deuterated methanol CHD₂OH (Methanol-D₂). Transition frequencies have an estimated uncertainty of about ±50 kHz. Albeit the complexity in the spectra, assignments were possible for a large number of a-type (ΔK = 0) transitions. In the course of the assignment process a strong c-type (ΔK = 1) Q-branch connecting two states of different symmetry species has been identified. This Q-branch assignment is significant because it is forbidden in the normal parent species CH₃OH. It becomes allowed in the current species due to the effects of the asymmetry introduced by the off-axis deuterium in the hindering potential to the internal rotation in the molecule. The assignments are rigorously confirmed using combination relations which required the measurement of some other related lines. To our knowledge this is the first time such symmetry breaking transitions are reported in CHD₂OH and in fact this is the first time the SMMW spectrum of CHD₂OH is being reported. Detailed spectral study of this molecule in the IR and FIR regions is in progress and will be reported elsewhere. Detailed study of the identification optically pumped FIR laser line is underway.     

Very high resolution far infrared synchrotron radiation spectrum of methanol-D1 (CH2DOH) in the first three torsional-vibrational modes

In our effort to systematically study the far infrared (FIR) spectra of asymmetrically mono deuterated methanol (CH₂DOH) and thereby obtain the transition wavenumbers with better and better accuracy (Mukhopadhyay, 2016a,b), the complete Fourier transform (FT) spectra from FIR to infrared (IR) vibrational bands (in the range 50–1190 cm⁻¹) have been re-recorded using the Synchrotron Radiation Source at the Canadian Light Sources in Saskatchewan, Canada. The resolution of the spectrum is unprecedented, reaching beyond the Doppler limited resolution as low as about 0.0008 cm⁻¹ with a signal to noise (S/N) ratio is many fold better than that can be obtained by commercially available FT spectrometer using thermal sources (e.g., Globar). Spectra were also recorded beyond 1190 cm⁻¹ to about 5000 cm⁻¹ at a somewhat lower resolution of 0.002–0.004 cm⁻¹. In this report the analysis of the b-type and c-type torsional - rotational spectra in the ground vibrational state corresponding to gauche- (e₁/o₁) to gauche- (e₁/o₁) and gauche- (e₁/o₁) to trans- (e₀) states in the ground vibrational state are reported and an atlas of the wavenumber for about 2500 FIR assigned absorption lines has been prepared. The transitions within a given sub-band are analyzed using state dependent expansion parameters and the Q-branch origins. The data from previous results (Mukhopadhyay, 2016a,b) along with the present work allowed a global analysis yielding a complete set of molecular parameters. The state dependent molecular parameters reproduce the experimental wavenumbers within experimental uncertainty. In addition, the sensitivity of the spectrum allowed observation of forbidden transitions previously unobserved and helped reassignment of rotational angular momentum quantum numbers of some ΔK = ±1, Q-branch transitions in highly excited states recently reported in the literature. To our knowledge the wavenumbers reported in the present work are the most accurate so far reported in the literature and represent the highest resolution spectra for this molecular species.     

Infrared spectrum involving forbidden transitions & coriolis interaction and identification of optically pumped far infrared laser lines in asymmetrically mono-deuterated methanol (Methanol-D1)

In this paper new type of ΔK = 2 and 0 transitions have been identified in the Fourier Transform spectrum of Methanol-D₁ (CH₂DOH). These transitions are normally forbidden but a “Coriolis” type interaction with nearby states is believed to be contributing sufficient transition strength through intensity borrowing effect. This is the first time such forbidden transitions are reported to be identified in the excited states, in this molecule. The present conjecture is supported by observation of a many strong allowed transitions to upper terminating levels which are seen to be highly perturbed. This conclusion has been reached by comparing calculated energy levels using known molecular parameters (Pearson et al., 2012; Coudert et al., 2014; El Hilali et al., 2011; Quade et al., 1998; Richard Quade, 1998, 1999; Mukhopadhyay, 1997) and the actually observed FIR lines. The upper levels are seen to be upshifted from expected position. A closer look at the calculated energy values seems to indicate a possible interaction between the above states and other proximate torsional–rotational states could occur. The possible candidates for the interacting level manifolds are narrowed down through the presence of the forbidden transition. We also take the opportunity to propose alternate rotational quantum numbers for some of the assignments recently reported in the literature (El Hilali et al., 2011). Some ambiguities are pointed out on the data and the reported analysis. There remain too many such irregularities and we propose to gather a large body assigned transitions in a future catalog. Assignments and relevant comments on optically pumped FIR laser radiation are also made.     

High resolution analysis of the rotational levels of the (0 0 0), (0 1 0), (1 0 0), (0 0 1), (0 2 0), (1 1 0) and (0 1 1) vibrational states of SO2

A high resolution (0.0018 cm⁻¹) Fourier transform instrument has been used to record the spectrum of an enriched ³⁴S (95.3%) sample of sulfur dioxide. A thorough analysis of the ν₂, 2ν₂ − ν₂, ν₁, ν₁ + ν₂ − ν₂, ν₃, ν₂ + ν₃ − ν₂, ν₁ + ν₂ and ν₂ + ν₃ bands has been carried out leading to a large set of assigned lines. From these lines ground state combination differences were obtained and fit together with the existing microwave, millimeter, and terahertz rotational lines. An improved set of ground state rotational constants were obtained. Next, the upper state rotational levels were fit. For the (0 1 0), (1 1 0) and (0 1 1) states, a simple Watson-type Hamiltonian sufficed. However, it was necessary to include explicitly interacting terms in the Hamiltonian matrix in order to fit the rotational levels of the (0 2 0), (1 0 0) and (1 0 1) states to within their experimental accuracy. More explicitly, it was necessary to use a ΔK = 2 term to model the Fermi interaction between the (0 2 0) and (1 0 0) levels and a ΔK = 3 term to model the Coriolis interaction between the (1 0 0) and (0 0 1) levels. Precise Hamiltonian constants were derived for the (0 0 0), (0 1 0), (1 0 0), (0 0 1), (0 2 0), (1 1 0) and (0 1 1) vibrational states.     

Light-induced frequency shifts for the lowest vibrational levels of ultracold Cs2 in the molecular pure long-range 0^-g state

The light-induced frequency shift(LIFS)of ultracold molecular ro-vibrational levels originates from the strong coupling of the atomic-scattering state and the bound-molecular state.In this paper,we present our experimental determination of the LIFSs of the lowest vibrational levels(v=0,1)in the purely long-range 0^-g state of ultracold cesium molecules.A high-resolution double photoassociation spectroscopy is developed,which serves as frequency ruler to measure the frequency shifts of the lowest molecular levels for Cs2.The experimental results are qualitatively consistent with the theoretical expectations.     

Inversion of the Ka = 0 and 1 rotational levels in the lowest excited vibrational state of HNCS

Fairly strong, regularly spaced absorption lines have been observed in the microwave spectrum of HNCS and assigned to b-type, K_a = 0 ← 1, Q-branch transitions arising from molecules in the lowest excited vibrational state. The Fortrat diagram of these lines has the appearance of a c-type Q branch, which is impossible in HNCS because of its symmetry. This anomalous b-type Q-branch spectrum is caused by strong a-type Coriolis interactions among the three low-lying bending modes; the K_a = 1 levels of the lowest excited vibrational state are perturbed and shifted lower in energy than the K_a = 0 levels for each J. This interpretation has been confirmed by the observation of P- and R-branch transitions associated with this Q branch. The band origin has been determined to be ?40 104.287 MHz (?1.3377 cm^?1). The inversion of the K_a = 0 and 1 energy levels is consistent with the interpretation of HNCS as a quasi-linear molecule.     

On the vibrational behaviour of cyanide adsorbed at Pt(1 1 1) and Pt(1 0 0) surfaces in alkaline solutions

This communication deals with the vibrational behaviour of cyanide adlayers formed on Pt(1 1 1) and Pt(1 0 0) surfaces in the electrochemical environment. In situ FTIR spectroscopy can be employed to follow the potential dependence of the C-N stretching frequency in acidic electrolytes with quite a low uncertainty. Owing to the stability of the cyanide adlayer in alkaline solutions, experiments performed in NaOH medium are usually perturbed by the significant overlapping of the reference and the sample FTIR spectra. Deconvolution of the spectra was carried out assuming a Lorentz oscillator. The procedure allowed to confirm that two potential regions with different band centre frequency tuning coexist for Pt(1 1 1)-CN in perchloric acid medium. Conversely, in the alkaline electrolyte a single tuning rate for the band position was found for both surfaces studied. The lack of reorientation of the C-N molecular axis together with the occurrence of a certain screening effect of negatively charged hydroxyl anions on the electric field at the interface could be at the origin of the different behaviour displayed in both electrolytic media.     

Barriers to internal rotation and tunnelling splittings of the torsional states in the HO(CH2)OH,DO(CH2)OH and DO(CH2)OD molecules

Torsional states caused by vibrations of hydroxyl groups in the methanediol molecule and its two deuterated analogues – DO(CH₂)OH and DO(CH₂)OD were analysed at MP2/cc-pVTZ and CCSD(T)/cc-pVQZ levels of theory. In the first case, 2D PES and 2D surfaces of kinematic coefficients were calculated with geometry optimisation for all other geometric parameters, and in the second case, only the energy of optimised configurations at the MP2/cc-pVTZ level of theory was determined. Then 2D PES was recounted to the complete basis set (CBS) limit by extrapolating the results of calculations at the MP2/cc-pVTZ and MP2/cc-pVQZ levels of theory The calculated values were then averaged over four equivalent points on the coordinate plane. Hamiltonian matrices were constructed using DVR and Fourier methods. After their subsequent diagonalization, the energies of the stationary torsional states were computed. Their classification by C_2V(M) and C_S(M) molecular symmetry groups has been performed. The splitting values due to the tunnelling of the thirty most deeply located torsional states in the three studied molecules were also determined. The torsional states, internal rotation barriers, and tunnelling frequencies in the molecules of methanediol and hydrogen trioxide were compared.     

The millimeter-wave spectrum of chlorine nitrate (ClONO2): The ν6 vibrational state

The pure rotational spectrum of chlorine nitrate in its v₆ = 1 excited vibrational state has been studied. A total of 2901 lines, with K_a extending to 33 in the ³⁵Cl isotopologue and 30 in the ³⁷Cl isotopologue, respectively, have been recorded and assigned. This analysis, along with our recently reported study of the ν₅/ν₆ν₉ dyad and the improved energy levels of ν₉ reported in this paper, should make possible accurate simulation of the corresponding ν₆ band and its complex hot band structure near 435 cm⁻¹.     

Experimental and theoretical analysis of the 5 pnpJ =0 e , 1 e , 2 e autoionizing spectrum of Sr

The even parity 5 pnpJ = 0, 1 and 2 doubly excited autoionizing states of strontium were investigated both experimentally and theoretically. Sr atoms in an atomic beam were excited through the two-step Isolated Core Excitation (ICE) scheme 5s^{2 1} S ₀ -λ ₁ → 5 sn'p ¹ P ₁ ( n' = 12-16)-λ ₂ → [5 p _3/2 np ] _J . The final ICE transition probes the [5 p _3/2 np ] _J resonances. However, the [5 p _1/2 np ] _J series below the 5 p _1/2 threshold were excited also due to their mixing with the [5 p _3/2 np ] _J perturbers. An extended energy region was covered below and above the 5 p _1/2 ionization limit by saturating the central ICE lobe and recording as many as possible “red” and “blue” secondary lobes. J identification was achieved by using mutually parallel and perpendicular linear polarizations of the laser beams. The ICE spectra were compared to those obtained by employing a two-step excitation scheme using the bound 4 d 5 p ¹ P ₁ valence state as an intermediate one. Final identification for very complex structures was achieved after comparison with theoretical energy level positions and excitation profiles produced by the R-matrix method combined with the multichannel quantum defect theory (MQDT) method. The agreement between theoretical and observed structures is quite satisfactory. Received 31 May 2000     

Infrared intensity analysis of CH2Cl2 and CD2Cl2 in vapour and liquid states

In the infrared spectra of molecules with more than one C-H bond the symmetric and antisymmetric stretching bonds often overlap, causing uncertainty in the intensity analysis. For CH₂Cl₂ and CD₂Cl₂ in the vapour state, the two bands overlap to such an extent that Straley who takes it as one band attributes it to antisymmetric stretching while Saekiet al assign it to the symmetric stretching. Following the method of analysis initiated in this laboratory, we have solved this problem by ultimately obtaining intensities separately forA ₁ andB ₂ species. The band is mostly due to the symmetric stretching, 0.06 out of the total of 0.31 contributing toB ₂. Thus, this gives a method of separating the intensities of bands which are highly overlapping. Presented at the Symposium on Crystallography and Crystal Physics, Osmania University, Hyderabad held on 5–7, December 1977.     

The far-infrared rotational spectrum of nitrous acid (HONO) and its deuterated species (DONO) studied by high-resolution Fourier-transform spectroscopy

In this paper, we present the first high-resolution (0.003 cm⁻¹) absorption measurements of the pure rotational spectra of nitrous acid (trans- and cis-HONO) and its deuterated species (trans- and cis-DONO) in the far-infrared region between 40 and 150 cm⁻¹. The spectra were first assigned based on rotational constants from previous studies in the microwave and mid-infrared regions. New rotational and centrifugal distortion constants were determined for all four species. The accuracy of the principal rotational constants was improved, and several quartic and sextic (and even a few octic) centrifugal distortion constants were obtained for the first time. Synthetic spectra calculated using the new constants of this study reproduce the observed spectra very well.     

Rotational spectrum of ONCl in the (0, 0, 1) and (0, 1, 0) vibrational states and “b” type spectrum in the ground state. Comparison of force field obtained by different combinations of experimental data

From the rotational spectrum of ONCl in (0, 0, 1) and (0, 1, 0) excited vibrational states the inertia defects in these states have been determined. The “b” type rotational spectrum in the ground state has also been measured allowing the determination of Δ⁰ and of all the first-order centrifugal distortion constants.It is shown that by using differences of inertia defects Δ₂ and Δ₃ together with centrifugal distortion constants which do not involve the planarity relations and with harmonic vibrational frequencies of two isotopic species, the harmonic vibrational frequencies of two other isotopic species can be satisfactorily predicted.By using only inertia defects differences Δ₂ and Δ₃ as extra data, a definite choice can be made among the three sets of force constants which equally well reproduce the harmonic frequencies of four isotopic species.     

The eight first vibrational states of the water molecule: measurements and analysis

In this work the spectrum of the water molecule has been the subject of extensive experimental and theoretical investigations. More than 1500 transitions have been assigned in a far infrared emission spectrum recorded in the 50-500 cm⁻¹ region and experimental rotational energies have been obtained for the second triad of interacting states, (0 3 0), (1 1 0), and (0 1 1), up to J=10 using flame spectroscopy. These new data along with a large data set of already published experimental rotational energies, high-resolution infrared transitions, and microwave lines, involving the eight first vibrational states, have been analyzed using the theoretical formalism developed for water in a previous paper (J. Mol. Spectrosc. 206 (2001) 83), which accounts for the anomalous centrifugal distortion as well as for the Fermi- and Coriolis-type couplings.